There is nothing magical about pensions versus ISAs, the UK’s two tax-free savings wrappers , that somehow enables pensions to break the laws of mathematics.
Both pensions and ISAs deliver one-shot tax relief , as well as allowing your savings to grow tax-free.
- Pensions give you the relief upfront, by rebating the tax you’d otherwise pay on your contributions.
- ISAs give you the tax break later, since you pay no tax when you cash in your ISA investments.
You’ll often hear people claim that pensions are better than ISAs because upfront relief is more valuable. “You have more money to compound over the years with a pension,” they say, which they claim gives pensions the edge.
But this is wrong – all things being equal.
Now, all things are rarely equal, and I’ll get to that in a minute.
But first the science bit.
Pension versus ISAs: A quick recap
- With a pension, you get tax relief on your contributions.
- If you pay 40% tax, say, then a £1,000 contribution costs just £600 of taxed income.
- You pay tax on the money you take out when you retire .
- With an ISA, you get no initial tax relief.
- Instead, you put some of your taxed salary  into the ISA.
- However, you do not have to pay tax on the money you withdraw later.
Mathematically speaking, there is no difference between these two situations, provided the tax rate is the same.
Proof that ISAs and pensions are the same, maths wise
Here’s some algebra to prove pensions and ISAs are equivalent – all things being equal.
Consider the variables:
- A lump sum investment of £x
- Tax rate of t%
- Annual growth of i%
- Investment period n years
With an ISA you get no initial tax relief, and you pay no tax on withdrawal.
The formula for how your money compounds over ‘n’ years is therefore simply:
- ISA = x * (1+i)^n
With a pension you get tax relief of t%, but you also pay t% tax when you withdraw the money later.
The formula for how your money compounds over ‘n’ years is:
- Pension = x/(1-t) * (1+i)^n * (1-t)
Now, (l-t)/(l-t) cancels out. This leaves us with:
= x * (1+i)^n
Which is exactly the same as the ISA!
This is why some prefer to use the phrase ‘tax deferment’ rather than ‘tax relief’ when talking about pensions. The relief you get upfront is cancelled by the tax you pay later – all things being equal.
A worked example of tax equivalence
Here’s an example of pensions versus ISAs with real numbers.
Consider a higher-rate taxpayer who:
- Sets aside £1,000 of his gross salary to invest every year
- Pays 40% tax
- Gets 10% a year growth on his investment
- Leaves it to compound for five years
- Draws an income of 5% a year in retirement
With the ISA, he is funding his contributions out of his taxed income.
Higher-rate tax is 40%, so our man’s £1,000 contribution is multiplied by (1-0.4=0.6) to reduce it by 40%, then compounded over five years, and then finally, he takes out 5% (so we multiply by 0.05).
- £1,000×0.6×1.1×1.1×1.1×1.1×1.1x.05 = £48.32
With the pension, our chap can put in the £1,000 from his salary tax-free. However, he must pay 40% tax at the back-end.
This time, we get:
Important caveat: Things are NOT equal
I’ve shown there’s no difference between an ISA and a pension from a pure maths standpoint.
But I said that was with ‘all things being equal’. And things aren’t equal!
Caveat 1: Lower-rate taxpayer in retirement
Most people pay a lower-rate of tax in retirement (0-20%). This can make a pension a better option than an ISA for higher-rate taxpayers who will be lower-rate taxpayers in retirement, because the rate they pay on withdrawing the money (20%) will be lower than the tax relief they got on when they put the money in (40%, or 45% for additional rate payers1  ).
In my worked example, instead of multiplying by 0.6 to represent the tax on withdrawal, as a lower-rate payer you’d multiply by 0.8, which gives a much higher income of £64.42.
But there’s more! You still have an annual income tax personal allowance  as a pensioner. So a good chunk of your pension income may not be taxed at all. (The first £11,000 at the time of writing, presuming no other taxable income streams are complicating matters.)
On the other hand, some of your personal allowance should be used up by (hopefully) a State Pension at some point in your retirement. The State Pension counts as taxable income.
As you can see the marginal tax rate you’ll pay can be very uncertain 15-20 years in advance.
Caveat 2: Tax-free lump sum with a pension
On this portion of your money you get tax relief going in, and yet can pay no tax on that 25% coming out later – the best of both worlds!
Again, this gives pensions an edge over ISAs.
Caveat 3: Employers pay into pensions, but not ISAs
Employers contribute  to pensions, which can be a substantial advantage, and there are National Insurance savings too.
Pensions are also better protected if you lose your job  and need to claim benefits.
Pensions versus ISAs: Same but different
In the old days – that is, three or four years ago – we’d now shift gears to talk about the huge and hidden downsides of pensions.
Gloomy organ music would rise up out of nowhere, an unseen wind would shutter the windows and plunge us into darkness, and we’d somberly recount the onerous restrictions on what you could actually do with your money that you’d saved into your pension when you were old enough to need it.
All that changed though with the 2014 Budget’s pension freedoms .
There are still some rules on what you can do with your pension pot – most particularly when you can get access to it. Currently you need to be 55, but that age climbs if you’re younger and many fear it will keep rising.
You do also need to be aware of the tax implications of different withdrawal strategies.
In contrast, with an ISA you can spend your accumulated money how and when you like. It’s always tax-free.
But still, when it comes to how you invest your pension pot once you’ve retired and how you withdraw it, most of the old strictures are gone.
Most dramatically, you’re no longer compelled to buy an annuity. You can instead invest your pension in other assets to create an income that suits you.
Famously, you can even withdraw the money to buy a Lamborghini  if that floats your boat.
Our contributor The Greybeard has been covering this brave new world of pensions and deaccumulation . Please do check his articles out.
The changes mean that most people on a fairly normal retirement path will conclude that a low-cost pension based around tracker funds  or an ETF portfolio  is the best vehicle for retirement savings.
My co-blogger The Accumulator certainly thinks pensions have the edge .
ISAs are still massively valuable for all-purpose savings. They can also back up your pension contributions, and diversify the risk of future governments fiddling with the rules.
In an ideal world you’d have both a pension and ISAs. But whatever you do make sure you’re using some sort of shelter to stop tax reducing  your investment returns.
Note: Older comments below may pre-date the pension freedoms. Check the dates! Also I’ve not gone into Lifetime ISAs, as there are signs that the government is already having second thoughts about the inherent inconsistencies in this halfway house. If they are implemented we’ll come back to them, so please do subscribe  for updates.
- But beware of reduced annual allowances  if you’re a high-earner. [↩ ]
- Technically it’s called a Pension Commencement Lump Sum, or PCLS. [↩ ]
- If you’re trying to retire in just ten years say, then the annual ISA contribution limits are going to be a snag. Make sure you’re fully up-to-speed on capital gains tax strategies  and the like. [↩ ]