Why would you want to unitize your portfolio? I mean life is short – and there’s a lot of good stuff on Netflix.

Well… maybe you’re a stock picker who wonders whether you’re beating the market?

Or perhaps you’re a passive investor keen to see how the returns from your DIY ETF portfolio compares to Vanguard’s LifeStrategy fund?

Whatever the motivation, you’ll need to track your performance versus active and index funds to know for sure.

And that means comparing your results calculated using the same methodology that they use – portfolio unitization or time-weighted returns.

If you think you’re a great investor but really you’re lagging the market by 3% a year, it will have a disastrous impact on your wealth compared to if you’d used index funds.

That’s not to mention the many hours wasted in fruitless research. (Unless you happen to enjoy it…)

Still want to know how you’re doing?

How to unitize your portfolio to track your returns

I believe the best way to track your returns is to unitize your portfolio.

Granted, you can use online portfolio tools or work out various numbers on-demand. But I think it’s better to take charge for yourself so you understand not just the numbers, but what is driving those numbers.

Moreover, it’s easy to do. You don’t have to pay a monthly subscription fee, nor worry about losing your data when that aging app is discontinued. 

To make it even easier we’ve created a unitized / time-weighted return spreadsheet to help you on your way.

Spread the word! You’ll find our example spreadsheet makes more sense after you’ve read the article that follows. But for now know there are two tabs – one to track cashflows and the other to track capital values and units. We’ve pre-populated the cells to illustrate how somebody might be tracking the ups and downs of their portfolio over a few years – as the market climbs and they add new money, receive dividends, and decide to withdraw some cash. Make a copy of the spreadsheet to delete our example data and start tracking your own.

What is unitization?

Unitization is the method used by fund managers who must account for money that flows in and out of their open-ended funds.

And because it’s the industry standard method for measuring returns, unitization means you can compare your performance with any existing fund.

You can also compare a unitized portfolio’s performance against a benchmark such as an index.

And unitization encourages you to keep decent records – also important if you’re trying not to kid yourself.

As physicist Richard Feynman warned: “The first principle is that you must not fool yourself, and you are the easiest person to fool.”

Why open-ended funds are called unit trusts

You are probably already familiar with unit pricing when it comes to funds.

If not, here’s a quick refresher.

When you invest your money into an open-ended fund, you buy a certain amount of units in that fund with your money.

For instance, let’s say I have £18,420.58 invested in the European Index Trust run by Fictitious Fund Co (FFC).

The FFC website tells me how it calculates this:

Number of units I own: 6,564.712
Unit price Buy/Sell: 280.6p/280.6p
Value: £18,420.58 (i.e. 280.6 pence x 6,564.712 units)

All investors in FFC’s European index fund would see exactly the same unit price.

However they will own different numbers of units, depending on how much they have invested.

Making more units

Whenever investors put additional money into the European Index Trust, FFC creates new units at the prevailing unit price.

The new money buys the right number of units at that price for the money invested.

For example, if the unit price were 280.6p, then investing £5,000 would buy you 1,781.9 additional units.

The new cash you’ve invested now comprises part of the assets of the unit trust, which offsets the creation of those new units.

The fund’s total Assets under Management (AUM) have increased, but the returns haven’t changed just because new money has been added. This is confirmed by the unchanged unit pricing.

Finally, the fund manager deploys your extra money to buy more holdings in order to keep the fund doing what it says on the tin.

In this example, he or she buys more shares to match the European Index.

Unit prices and new money

The crucial point is that adding new money does not change the price of a unit.

Only gains and losses on investments, dividends and interest, and costs that are charged against the portfolio’s assets will change the price of a unit.

For example, if the companies owned by the European Index fund rose 10% in value, then the unit price would be expected to increase by 10%, too.

So here the new unit cost would be:

280.6*1.1 = 308.66p.

Measuring changes in the value of units like this – as opposed to measuring the total monetary size of the fund – enables the manager to maintain a consistent record of performance.

A record that is not distorted by money coming in and going out.

Also, when an investor wants to cash out from the fund, there’s no confusion about what percentage of the assets they own or anything like that.

They’ll own a certain number of units. To cash out, they sell them back to the fund manager at the prevailing unit price.

For instance, let’s say you own 600 units.

At 280.6p per unit, you’d cash out with:

£2.806 x 600 = £1,683.60

By unitizing your portfolio, you can use the same principle to measure your own returns – whether you’re saving and investing extra cash or you’re withdrawing money from the portfolio.

How to unitize your portfolio

So far, so boring.

Well, we are talking about accountancy here!

I’ll level with you. Things aren’t going to get any more exciting.

However the good news is that unitizing your portfolio is a very straightforward process. 

1. First decide on an arbitrary unit value

The first thing you need to do is to decide what one unit in ‘your fund’ is worth.

It’s a totally arbitrary decision, as it will just be used as the base for future return calculations.

Many people choose £1.

I chose £100 for egomaniacal reasons.

2. Calculate how many units you currently have

As it’s Year Zero for unitizing your returns, you need to work out how many units you currently have.

This is based on the total value of everything in the portfolio you’re tracking, together with the unit value you just came up with.

You simply divide the former by the latter.

Let’s say your portfolio is £50,000 and your unit value is £100.

This means you have 500 units to begin with, like so:

£50,000/£100 = 500 units

Create a column on your spreadsheet to track the unit number. 

Pop in another column to track the value of each unit:

£50,000/500 units = £100 unit value. Think of this column as the index value of your portfolio. It starts at 100 points. 

As time goes on, you can chart your progress by plotting your (hopefully) growing unit/index values on a graph. (See the Portfolio unit value column on our accompanying spreadsheet.)

I track these numbers on my own spreadsheet. It tells me what my portfolio is worth right now, what one unit is worth, and how many units I have.

From this it also works out and tells me my returns over various periods.

3. If you don’t add new money you can now easily track your returns

Let’s say you never did add or remove another penny from your portfolio.

You know how many units you have, and you know the starting unit value.

Working out your unitized returns from here is a doddle.

For example, let’s say your portfolio increases to £60,000.

The unit value is now:

£60,000/500 = £120

Your return to-date is the change in unit value.

£120-£100/£100 = 20%

However you hardly needed to unitize to see that!

4. Adjust your total units as you add new money

The whole point of unitizing is to properly take into account money added or removed from the portfolio.

Every time you add new money, you need to calculate and take note of the value of one unit.

For instance, let’s say that when your portfolio hits £60,000 you decide this investing lark is a piece of cake, and so decide to add in another £6,000.

The unit value before the additional cash is added, as above, is £120.

Now we need to calculate how many units our new money buys:

New money added / unit cost = number of new units
£6,000/ £120 = 50 new units

This means your £66,000 portfolio now comprises 550 units.

You can see this calculation in our dummy spreadsheet. The new £6,000 is inputted into the Cashflow tab, and you can see the extra 50 units show up on the Unitized return tab – Unit change column. 

5. Keeping ‘buying’ new units as you add money

This process is simply repeated over your investing lifetime.

Let’s say the value of your portfolio increases to £69,850, and you decide to add an ISA contribution of £15,240.

First:

Unit value = portfolio value / number of units
Unit value = £69,850/550
And so…
Unit value = £127

Number of new units that £15,240 buys:

New money added/ unit cost = number of new units
£15,240/£127 = 120 new units

With the new ISA money your portfolio is now worth £85,090, and is comprised of 670 units (that is, 550+120).

As always you note down the total unit number for next time.

6. What happens when you remove some money?

When money is removed entirely from the portfolio, the principle is exactly the same as when money as added. The number of units changes as a consequence, but not the unit value.

You are effectively ‘selling’ units in your own fund to free up the cash. Obviously this procedure doesn’t change the returns you have achieved on the mix of assets you happen to hold.

For example, let’s say your portfolio continues to motor on and breaks through six figures to hit £100,165.

At this point you get collywobbles (I told you there was a downside to tracking your returns) and you decide to spend £10,000 of it while you’ve still got your teeth.

You know from your records that your portfolio currently consists of 670 units.

This means the unit value currently is:

£100,165/670= £149.50

You decide to remove £10,016.50 from the portfolio to keep the sums simple:

£10,016.50/£149.50 = 67 units

After the withdrawal you have £90,148.50 in your portfolio represented by 603 units (670-67).

The sale is noted in the Withdrawals column of our spreadsheet in the Cashflow tab. The liquidated units are tracked in the Unitized return tab. 

7. Work out your unitized return at any point

At any moment in time you can see exactly what your return is by looking at your unit value.

For instance, let’s say that after all of the above, your portfolio ends the year with a value of £90,450.

Your unit value is:

£90,450/603= £150

So your unitized return since you unitized your portfolio is:

£150-£100/£100 = 50%

This is the return that you can compare with trackers and other funds and benchmarks that report their returns over the same period.

Let’s say at the end of next year a unit was worth £160.

You started the period with a unit value of £150. So your return over the year is:

£160-150/150= 6.67%

You see how easy it is to calculate and note down your annual return figures every year.

What about expenses?

If you cover costs like broker fees, stamp duty, and accrued interest with external money that you add to your investment account, then these amounts should be included in your incoming cashflows. 

The treatment is different if you pay your costs by selling assets, or if you use dividends, or other cash lying around the portfolio.

In the latter case, the expenditure is taken care of by a reduction in your portfolio’s value. You needn’t even note when these costs are paid. Your portfolio will simply be smaller than otherwise next time you record its value. If all prices remained the same then you’d see that a small loss had been inflicted by the fees.

As ever, fees reduce returns and higher costs are a greater drag factor than lower ones. 

What about dividends, interest, redemptions, spin-offs, and so on?

You needn’t worry about these so long as they’re retained within your portfolio. 

The number of units you own doesn’t change because you were paid a dividend – no more than if one of your shares went up by 20p.

But your units do now represent more assets, in the form of that extra dividend cash. That increases the value of each of your units.

You can see this play out in the dummy spreadsheet when the portfolio receives £3,000 worth of dividends on 1 January 2026. (Yes, this is Doctor Who’s portfolio.) 

The unit value rises from 160 to 164.98 and the portfolio gains 3.11%. 

However, if you withdraw any of this income from your investment account then it should be logged as an outflow. 

Our sample spreadsheet books a £1,000 dividend withdrawal on 2 Jan 2026. The value of the portfolio decreases but it doesn’t count as a loss because the number of units is reduced to compensate. 

Hmm, unitization sounds like a lot of work

It’s really not, once you’ve set it up properly.

My spreadsheet tells me my current portfolio and unit value at any time.

A sheet also tracks money added and subtracted over the year, and calculates the number of units added or subtracted when I do so. They get added to the ongoing tally.

At the end of the year I simply record all the relevant values for my records. (I also export a snapshot of the spreadsheet as a PDF to serve as an archive).

Then, on the first trading day of the New Year, I hand-update the spreadsheet with my starting unit value and the total number of units.

This makes it easy to see and record my discrete total return figures for every year.

What if I have multiple dealing accounts, SIPPs, and the like?

I track all my different holdings on one spreadsheet.

Then I unitize the returns on this entire portfolio, and also track expenses, portfolio turnover, and other interesting figures across the entire piece. If you take monthly snapshots you can track your volatility, too. 

This is exactly how I measure my own total returns across half a dozen different platforms and brokers.

There’s not a lot of point in tracking the returns in a SIPP separately from returns in an ISA, in my view.

Ultimately it’s all your net worth. They’re just different baskets.

However if you did want to track how particular accounts are doing – perhaps because you employ different investing strategies in one versus another – then you could create separate spreadsheets to follow them.

You’d also have to track separate money flows in and out of each them, and generate unitized return figures for each ‘pot’ of cash.

Remember, you’d still want to unitize the entire portfolio to properly track your overall returns. (Rather than, say, averaging the returns on the different accounts, as this would not account for the different amount of money in each – though you could create a weighted average I suppose).

Time-weighted returns versus money-weighted returns

There are many different ways of calculating returns. They all have value in different circumstances. And they usually deliver different numbers.

Unitization offers a time-weighted return while the main alternative uses the XIRR Excel function to calculate your money-weighted return. 

• Time-weighted returns – all time periods are weighted equally, irrespective of how much money is invested when. Unitization tells you the underlying investment performance, and strips out the impact of money flowing in and out. This is the best way to compare your results against other portfolios, funds, indices, and even rival assets like cash in the bank or the price of Bitcoin.  

• Money-weighted returns – this means that time periods in which more money is invested have more of an impact on the overall return than equivalent time periods in which less money is invested. So doubling your first £50 does not count for as much as doubling £500,000 does later on.  

Monevator reader John Hill’s excellent comment below sheds additional light on the two measures with some illuminating examples. 

Getting the measure of market timing

XIRR calculates the Annualised Internal Rate of Return on a portfolio. The gist is that you supply the XIRR function with a column in your spreadsheet that lists these cash additions and withdrawals. The function then uses an iterative process to hone in on your returns.

It makes sense for the fund industry to use unitization. That’s because a fund manager typically has no control over when money is added or removed from their fund – it comes from the fund’s customers – and also because it’s the choice and performance of the underlying assets that matters when evaluating how skilful a manager is. (That’s the same reason I unitize my returns).

However some would argue that a money-weighted return like XIRR makes more sense from the perspective of a private investor. You are in control of money flows and what matters to you is your personal rate of return.

Many private investors derail their results with poor market timing. But by calculating and comparing both the unitized return and a money-weighted return you can spot the impact of poor (or – who knows – maybe good) market decisions timing on your portfolio.

The Henry Wirth investing blog explains:

• If your money-weighted return rate is greater than your time-weighted return rate, then your market timing is adding value to your portfolio.

• If your time-weighted return rate is greater than your money-weighted return rate, then your market timing is subtracting value from your portfolio.

The Accumulator tracks both. Read his companion post on how to calculate your money-weighted return. 

Do it for yourself

Personally I think if you’re going to keep track of the money flows in and out of your account, then you might as well go the whole hog and unitize your portfolio.

Once you’ve setup a spreadsheet to do the sums it’s very easy to stay on top of things. Moreover you’ll have the satisfaction of knowing your returns are directly comparable with those reported by fund managers.

That’s not to say there’s a right or wrong way to measure returns.

It all depends on context, and on knowing what you’re measuring and why.

Also remember that in itself a return figure tells you nothing about the volatility or risk you took to get those returns. Nor about the maximum troughs (aka drawdown, or losses at the portfolio level) that you endured along the way.

But if you unitize your portfolio and keep records of, say, the daily unit price, then you can track that sort of thing for yourself if you’re so inclined.

Indeed, once you’ve unitized your portfolio, you can go crazy if you want to and use it as the basis for calculating all kinds of extra stuff – such as the Sharpe Ratio that might help you understand if your returns are down to skill or risk taking.

Who knows – if you’re young and feisty, maybe you could even include your unitized returns in your cover letter asking for a job with Ficticious Fund Co!

Credit to The Accumulator for the unitization spreadsheet he made to accompany this update. Many thanks TA! Please let him know if you spot any errors via the comments below… 😉