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Illustration of a crystal ball as metaphor for using the Rule of 300 to gaze into your financial future.

The Rule of 300 is a shortcut that enables you to estimate how much money you’ll need for retirement or to achieve financial independence.

Even more excitingly, it enables you to estimate what any particular line item in your budget will require in terms of capital funding.

That’s right! The rule of 300 turns amorphous future you into a flesh and blood person with their own wants, needs, and bank statements.

And if future you wants – or needs – a monthly subscription to a luxury hot chocolate delivery service, then the Rule of 300 will tell you how much you’ll need to have saved up to pay for it.

Most of us find it hard to imagine paying for stuff several decades hence. But the Rule of 300 bends the space-time continuum to make it easier.

Basically right but specifically wrong

Let’s get one thing straight upfront. The Rule of 300 is not a scientific law that can’t be broken. It will probably always be off a bit. It’s just a rule of thumb.

Some of the assumptions behind the Rule of 300 are open to debate.

Moreover, thinking we can predict exactly what we’ll be paying for in 30 years’ time – from robot insurance to our annual getaway to the moon – is delusional.

But as always with investing: what’s the alternative?

All forecasting methods have downsides. Few compensate by being as simple as the Rule of 300.

We’ll return to the caveats later. Once you know what assumptions you disagree with, you can replace them with your own guesswork.

Let’s first outline the rule as it stands.

What is the Rule of 300?

The Rule of 300 is dead simple. To use it you need only two numbers – and one of them is always 300.

Take your monthly spending. Multiply it by 300. The result is how much you’ll need to have saved up to keep living like you do today after you quit your job.

Let’s say you currently spend £3,000 a month.

£3,000 x 300 = £900,000

The Rule of 300 says you’ll need £900,000 to quit work and still pay your bills.

(Or to tell The Man to go hang. Or to safely smirk in meetings. To swap your job to do something less boring for money instead. Or to keep loving your job with a safety buffer. You decide!)

Be sure to multiply 300 by your monthly expenditure today. Not by your monthly salary, or a guess at what things will cost in 20 years, or by two-thirds of your income, or anything else.

Simply enter your expenditure as it stands. The Rule of 300 tells you what you’ll need to have saved to keep spending this amount from your capital. (Probably!)

Do not include any regular ISA or pension contributions in your budget. For the purposes of this calculation we’re assuming you stop saving and start spending.

A spartan guide to using the Rule of 300

The Rule of 300 is the easiest maths you’ll ever do in personal finance. But to save you even more bother, here’s a table that shows how much you’ll need saved according to the Rule of 300, based on various monthly expenditures:

Current spend (monthly) Capital required
£750 £225,000
£1,000 £300,000
£1,500 £450,000
£3,000 £900,000
£5,000 £1,500,000
£10,000 £3,000,000

Source: Author’s calculations

Depending on your lifestyle and your penchant for caviar and avocado on toast, those numbers may seem dauntingly high or very achievable.

But are you in the “HOW MUCH?” camp? Then the Rule of 300 is extra useful. It helps you see what your monthly spending habits will cost you in capital terms.

Let’s say you spend £12 a month on Amazon’s music streaming service. Multiply that by £300, and voila! You can see you need £3,600 saved today to keep the music playing indefinitely.

Not so bad, perhaps. However you may have other more onerous commitments:

Spending Monthly cost Capital required
Gym £30 £9,000
Premium AI tool £50 £15,000
Golf club £150 £45,000
Weekly meal out £250 £75,000
Fancy car on PCP £500 £150,000
Monthly mini-break £800 £240,000

Source: Author’s research (and bills)

I’m not judging. If your idea of retirement bliss is playing golf every day, then something has gone badly wrong if you’re not planning on paying for golf club membership.

However by looking through the lens of the Rule of 300, you might be motivated to cut back those things you don’t care about so much. This way you can reduce how much you need to save for financial freedom.

Maybe you were happy paying £10 a month for a Disney+ subscription when your kids were young. But now they prefer YouTube and you’re done with the Star Wars spin-offs.

Cancel the Disney subscription and that’s £3,000 less you’ll need saved up before you can declare financial freedom.

(Obviously you should be doubling down on your Monevator membership, though. We’ll keep you on the straight and narrow…)

The safe withdrawal rate (and the caveats)

The maths behind the Rule of 300 is based on a safe withdrawal rate (SWR) of 4% a year.

As you probably know, the SWR is said to be the money you can spend every year from your portfolio without (too much) risk of it running out before you die.

Here’s how the Rule of 300 works. Let’s say your monthly expenditure is £2,000. Over a year that’s 12 x £2,000 = £24,000. To find the capital required to fund that with a SWR of 4% we must solve (4% of Capital = £24,000) which is equivalent to (Capital = £24,000/(4/100)) which works out at £600,000. Alternatively, the Rule of 300 says multiply £2,000 x 30 0= £600,000. Ta-dah! Same!

Now, to say the safe withdrawal rate is controversial is an understatement. It’s the personal finance equivalent of the Kennedy assassination. People take it to mean different things, some of which may be contrary to the original research.

Some people are sceptical because it’s based on US investment returns for starters, which have been strong versus the global average. They say 4% is too high.

Others believe that the strong equity returns we’ve enjoyed for over a decade may mean future return expectations (and hence the SWR) should be lower.

And yet others believe 4% is too pessimistic. Bond yields have risen a lot. And anyway, the 4% rule was always too stingy in most scenarios, they argue.

Newer thinking – and our own Accumulator – even claims the SWR strategy can be improved by holding extra assets and using a variable withdrawal strategy.

Finally, some investing Luddites like me presume we’ll never touch our capital, but rather live off our income. We often coincidentally target an income yield of around 4%, even though the SWR research was based on spending everything.

Roll your own Rule of Whatever

I’m not proposing to win the SWR debate today. Just know that you can tweak the Rule of 300 to suit your own beliefs by reworking the maths to suit.

  • Want to target 5% a year as your withdrawal rate? Then you can use a ‘Rule of 240’ to estimate how big your pot must be.
  • Think 3% is more like it? For you it’s the ‘Rule of 400’.

Personally though, I’m sticking to the Rule of 300.

You’ll read all kinds of authoritative-sounding comments about what is the best number to use for either the SWR or as a rule of 300 multiplier.

Reflect on them, certainly. But understand that nobody knows, because we can’t be sure how our investments will pan out, how long we’ll live, nor how much money will really be required in the future for a decent standard of living.

Anyway, it’s only a rule of thumb. Keep it simple, Sherlock.

Not one rule to rule them all

Despite my rather analytical education, I’m not one for precise modelling in anything other than the underwear department.

Personally I don’t track my expenses or stick to a budget. I prefer to keep a rough idea of cash flows in my head.

I’m also not one for working out the exact amount of capital a person needs to target for some potential retirement in 23 years and three months’ time.

Back when I was still on my path to FIRE, I did sometimes look at what was needed to replace my income, but only as a ready reckoner. (This method targets pre-tax salary, unlike the Rule of 300’s after-tax spending. Both have their uses.)

I’ve nothing against precision, if that’s your bag. There are pros and cons to most approaches, and we can all learn from each other.

However even if you’re more particular than Dr Spock, note that the Rule of 300 demands zero effort in your everyday thinking.

You may have a 30,000-cell spreadsheet at home in the lab, but the Rule of 300 can still be a useful shortcut.

Much better than nothing

Most people don’t even have a financial plan written on the back of a napkin. They haven’t the foggiest what they’ll need to have stashed away for when they no longer receive a regular pay cheque.

Even high-net-worth individuals can seem deluded, while many of the less wealthy appear to think they’ll enjoy round-the-world cruises on the back of saving £50 a month.

At the other end of the spectrum, some people assume they’ll need so much money put away that ever stopping working is unrealistic.

Does any of that sound like you, or someone you know? Then the Rule of 300 can be a good start in getting a grip on things.

I repeat, it’s not a scientific law.

But in terms of changing how you think about your own financial needs, the Rule of 300 might be as significant for you as that falling apple was for Sir Isaac Newton!

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Weekend reading: Sunny side up

Weekend reading: Sunny side up post image

The first Weekend Reading every month can be read by anyone on the Monevator website. Subscribe for free to our email newsletter or become a member to ensure you see the rest.

Oil prices continue to bounce about with every speech and social media post put out by the Iran war’s belligerents [writes The Frugalist, who has the reins this weekend].

But the overall trend for prices is upwards. And that means increasing financial pressure on energy-intensive businesses and the electricity grid more generally.

Especially when you consider that the Strait of Hormuz normally carries a fifth of liquefied natural gas (LNG) exports.

Think back to 2022 – LNG was cited as a key solution to the challenge of weaning off Russian gas imports.

Oh dear!

President Trump has ​praised​ the UAE’s decision this week to leave OPEC. But whatever happens with the oil cartel is unlikely to reverse the prices for gas and oil while conflict continues in Ukraine and Iran.

Besides, we have known for a long time that with growing global energy demand, a limited supply, and the increasing expense of extraction, fossil fuel prices would likely increase.

Okay, there might be the occasional reprieve. (More fracking, anyone?) But oil is never going to be cheap and abundant again.

Heating hurts

The situation is worse if you rely on physical fuel delivery to heat your home.

The UK government can’t fix the geopolitical issues, but at least it has expanded its Boiler Upgrade Scheme. This will now provide up to £9,000 in grants for households that use heating oil or liquefied petroleum gas to switch to heat pumps. This is separate from the direct funding for affected households that comes via local authorities.

How many such houses will prove suitable for getting the best out of a heat pump is a different question, however.

Can solar rescue us?

I’ve looked into solar myself on multiple occasions. Not because it makes a compelling alternative to investing in a global ETF, but because I like the principle of DIY-ing my own energy production. Saving on energy bills would justify the expenditure.

Now, solar panels have been plummeting in price. But installation costs are still a problem.

In fact when it comes to my own house, the scaffolding is so complex that I’d be several thousand pounds down before I’d even bought a panel.

Germany has led the way with a cheap and cheerful alternative – plug-in solar, where panels are plugged into an inverter and then directly into your mains. The electricity generated then flows to where it’s needed, without electricians, dedicated circuits, or formal declarations.

You’re free to put such panels on fences, shed roofs, or even to mount them on a wooden frame. (I can foresee my DIY skills and a large bucket of nails coming in handy again!)

The media has been getting into the question of whether plug-in solar is economically worthwhile.

But other, more thorny issues remain. Such as whether the panels present a safety risk – especially given British electrics have oddities that other countries haven’t had to worry about.

Solar flares

I’ve noticed more than a few people seem to have decided to jump straight in with plug-in solar, even before government legalisation. Many vendors report they’ve sold out.

This may prove premature. I expect home insurers will be paying especially close attention to fires with large claims attached to see if unapproved inverters were plugged into the mains.

Also, if plug-in solar is only an option for homeowners and not the rental sector, then that will limit their beneficial impact. Figuring out a balance between making plug-in solar safe, not exposing landlords to liability, and enabling renters to install their own panels will be tricky. And I expect the government will still get some flak for not doing it quickly or safely enough.

Admittedly, fitting a few hundred watts of solar panels to hundreds of thousands – even millions – more homes won’t instantly get us off fossil fuels.

But even if it looks like plug-in solar will take a few years to pay off financially, as soon as the standards are approved and the safety aspects sorted, I’ll be at the front of the supermarket queue for my kit.

Hopefully, just in time to pair some panels with the summer BBQ.

On that note, I hope you have a great Saturday!

[continue reading…]

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Handbags at the dawn of the AI era [Members]

Handbags at the dawn of the AI era [Members] post image

The year is 2050. It’s five years since the US president handed over the nuclear launch codes to a possibly-sentient artificial intelligence. More tangibly, the AI revolution is all around us in clean and decarbonated air, abundant crops, and the banishing of cancers that slew millions just a generation ago.

Of course, half the world’s adults have no job – besides charity and volunteering – and half again of the rest ‘work’ in the same way spouses of London bankers used to run unprofitable art galleries in the Cotswolds.

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Cash total returns: a long run index for DIY investors

If there’s one asset we all definitely hold, it’s cash. So it’s odd that there isn’t a long-run cash index available – one that we can use to compare other investments against.

Academics approximate returns to cash by resorting to treasury bill or money market rates. But what might a savvy UK investor have achieved with money in the bank?

Monevator is devoted to DIY investing after all, and so an everyday cash savings index would better reflect the experience of individual investors. It would also form a useful reference point for future expectations.

And so without further ado (I’ve always wanted to say that!) I present the Monevator cash total returns index.

A UK cash savings index

Our new cash index tracks the total return of UK savings accounts based on monthly interest rate figures going back to 1900.

I’ve relied upon three sources:

My profuse thanks and additional hat-tips go to Monevator readers Alan Stocker, who suggested using the BSA and MSE sources, and Snowman, whose ongoing comments provided the motivational juice to plough through scads of dusty old interest rate records.

I’ll explain the decisions I’ve made in constructing the index at the end of the article. But first it’s high time I presented the facts on cash savings in the UK.

Spoiler: they’re not pretty.

The money illusion

The green cash uplands shown in the graph below represent the comforting sight of interest piling on interest. But the wavy red line that goes more or less nowhere is the return on cash after inflation:

Data from Millennium of Macroeconomic Data for the UK, 1Building Societies Association (BSA) Yearbook, Money Saving Expert, and ONS. April 2026.

The annualised real return on UK cash savings is 0.1% for the period 1900-2025. Miserable!

It’s a performance that stacks up poorly against other mainstream asset classes:

  • The money market annualised return is 0.4% (0.3% after fees)
  • All stocks gilts is 0.8% (0.7% after fees)
  • World equities is 5.6% (5.5% after fees)

In a nutshell, those returns and the chart above explain why we urge readers not to put everything into cash. The green stuff barely scrapes past against inflation over time.

Of course cash is not the worst place to be over some shorter periods, as we saw in 2022. And there are good reasons to always keep some readies in reserve.

However holding a large wedge will likely cost you as the years turn into decades.

The silent hissing of a slow puncture, or the quiet boiling of that unlucky frog come to mind.

Hard times

The next chart highlights cash’s longest losing streaks in real terms – including a 72-year whopper:

We’ve shared some godawful charts over the years on Monevator. But this one is right up there.

The red zones show you the length and depth of cash drawdowns, as viewed through inflation-adjusted googles. They demonstrate that cash can be a perilous place to store your wealth if you overly rely on it.

The same is true of all asset classes, admittedly. But cash is deceptive because it looks so stable in nominal terms.

However as the chart shows, cash can periodically inflict huge losses – and the culprit isn’t hard to find:

Inflation protection is costly

As we’ve all experienced lately, the cash-gobbling monster of inflation isn’t a blight that’s faded into history like smallpox, or grit in your codpiece.

Cast your eyes back to the cyan growth line in our chart above. Cash has only performed well in real terms over a few short periods: namely 1921 to 1933 and 1982 to 2008.

On both occasions you could have done better in bonds.

The not-so-flash crash

Here’s the full drawdown chart for cash’s nastiest ever bear market.

The record shows:

  • Cash spent over 72 years in negative territory
  • It took 48 years to sink to the bottom
  • Losses peaked at -58% in April 1981
  • The recovery took another 24 years until December 2005

Money markets experienced similarly severe losses. UK government bonds suffered an even deeper, if shorter, drawdown. (See our previous retelling of the tale of the UK’s worst ever bond market crash. Prepare a stiff drink.)

Essentially, successive UK governments failed to control inflation. That wrecked the real returns from fixed income assets.

The red gouge above partly explains why my grandparents – born around 1910 – were so hard up. All they had were savings with the Post Office. But whatever they put away was murdered by inflation. Especially in the early 1940s, the early 1950s and, most savagely, in the 1970s.

Yet go back to the first chart in this article and cash’s nominal return curve betrays no hint of these losses that lasted a lifetime.

Cash after the Global Financial Crisis

Let’s fast forward.

The competitive savings market we enjoy today was unknown to previous generations.

British savers had few options until the cosy arrangements of our banks and building societies were broken up by deregulation from 1987 onwards.

Two decades later, the retail savings market was flourishing on the eve of the Credit Crunch, as documented by Money Saving Expert’s empowering weekly emails.

Easy-access rates topped 6% as the first rumbles of the oncoming storm rolled across the consumer landscape in 2007. 2

But within a few months, Britain experienced its first retail bank run in 140 years. Keystone institutions teetered, and the economy locked-up.

The Bank of England cut rates to historic lows, and real cash returns fell into the red:

Since January 2009, cash has been under water for all but one month up to the time of writing. That’s 17 years of drawdown and counting.

The chart shows that cash wasn’t a save haven either when interest rates were slashed to near-zero, nor when they rebounded post-Covid.

Indeed, the jagged plunge to the latest cash trough (-15% in May 2023) was a direct consequence of the 2021-23 inflationary surge. The only good thing about cash during the recent cost-of-living crisis was its drawdown wasn’t as bad as bonds.

Frankly, neither cash nor bonds are the place to be when inflation breaks loose.

Please read our previous hunt for the best inflation hedge for more.

Conflict of interest

Before I embarked on this project, I had thought a fleet-footed saver may have beaten money market rates. But the data says otherwise.

The next chart shows how British savers have mostly lagged the official Bank of England rate since 1900. (Money market returns usually track the central bank rate like a lovelorn teenager):

There’s a lot of economic history packed into this chart, but the takeaway is that savers have only outperformed the going rate during two eras.

One was upon the outbreak of World War 2 up until Churchill’s re-election as Prime Minister in October 1951.

The other shows up in the MSE era of consumer choice from 2004. Up until the Global Financial Crisis, the green cash rate tracks ahead of the red Bank Rate as savers were offered very generous terms – the likes of which haven’t been seen since.

The Bank Rate is then slashed from 5% in September 2008 to just half-a-percent by March 2009, as the scale of the crisis became clear.

Still, if you kept your job, a chunky rate tart’s premium emerged as different banks and building societies needed to suck in cash periodically to balance their books.

Switching to whichever institution was most in distress at the time was perhaps not my soberest ever financial move (reader, I was a rate tart) but hey, the British Government was playing backstop so it seemed okay.

In my view though, the savvy saver’s edge has hardly been worth the effort since 2022, though the premium perked up a little in 2025 – as you can see at the tail end of the chart.

Inside the cash total return index

There were a surprising number of decisions to make in assembling the index – specifically in the MSE-powered ‘best buy’ era.

The most important thing to say is that the index is composed of the compound interest rates for short-notice savings deposit accounts.

Up to October 1939 – We use the ‘Interest rate on sight deposit accounts’. The Bank of England defines a sight deposit account as:

…where the depositor has access to the entire balance of the deposit, without incurring any penalty, either on demand or by close of business the day following that on which the deposit was made.

November 1939 to March 2004 – Interest figures come from the rates on ordinary shares accounts provided by the Building Societies Association. An ordinary shares account was just a standard savings account accessible using a passbook. (Ask your grandparents. Or me! I had a Post Office passbook account from childhood until I looted it as a desperate 21-year-old trying to make rent.)

April 2004 to present day – The best interest rate collated by Money Saving Expert at the end of each month, provided the account fulfils the following criteria:

FSCS protected (or European equivalent schemes prior to Brexit).

95 days or less notice required. This provision bears comparison with historical treasury bill rates which are typically for 3-month bills.

Introductory rates are included so long as they last at least six months.

Exclusions:

Cash ISA accounts due to historically severe caps on balances.

Fixed term rates – these accounts are subject to interest rate risk.

Accounts that limit withdrawals to fewer than 12 per year or impose interest rate penalties for withdrawals.

Minimum deposit requirements of greater than £1,000 or a maximum balance of less than £85,000.

Current accounts, because they’re typically subject to restrictive terms and conditions including tight caps on bonus interest rates.

Exclusively postal or in-branch accounts.

Cash back bonuses.

Tax rates and fees as per standard practice for indices.

The notional saver

Indices by definition are based on a set of guidelines that simplify the real world in order to produce a snapshot of a market.

The Monevator cash total return index is based on what a switched-on UK retail saver could have earned on liquid cash savings from 1900 to the present day.

My notional saver paid attention to rates and moved their money to the best available product. But they did not use exotic or highly restrictive products.

They’re not the average saver, but neither do they have unlimited time and the motivation to pursue every savings avenue either.

Crucially, the index needs to be comparable with retail investment opportunities where an investor can commit almost as little or as much as they like to any given asset class.

For that reason, I’ve only admitted accounts that allow for low minimum balances and high maximum balances.

I’ve also ruled out fixed-term savings because they contain embedded interest rate risk. 3

In the modern era, financial institutions have come up with every wheeze they can think of to top the best-buy tables for long enough to hit their targets, whilst avoiding attracting so much cash that it craters their bottom line.

So I’ve had to filter out much of that fiendishness in order to balance the features of a genuinely desirable cash product: liquidity, accessibility, and competitive interest rate.

Finally, I’m not making a claim about what any individual could have earned. The index is beatable if, for example, you took term risk at the right time, or used interest-boosting techniques like current account stacking.

(Current account stacking enables a saver to jack-up their return – and partially circumvent balance caps – by opening multiple accounts that pay sweet rates of interest on restricted amounts of cash. Perhaps you opened ten accounts, perhaps you opened 20. It was a viable strategy for juicing your cash returns in the ZIRP era. It didn’t move the needle as much as I hoped when I ran the numbers, though. But that’s another story.)

Alright, that’s it for now. I’m very much looking forward to the thoughts, reactions, and critiques of the Monevator Massive. And I reserve the right to adjust the index in light of any bright ideas you have!

Take it steady,

The Accumulator

  1. Thomas R, Dimsdale N. 2017. “A Millennium of Macroeconomic Data for the UK.” Bank of England.[↩]
  2. You could even bag yourself 8% on balances of up to £2,500 via an Abbey National current account.[↩]
  3. That is to say, adverse interest rate moves will leave you stuck in an uncompetitive product from time-to-time.[↩]
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