S&P 500 calculator
This calculator will not tell you what the index has returned. It will tell you what return your plan needs, how wide the range of answers is, and what the dollar does to it.
Calculator
Your plan, the return it would need, and the range around it
What this plan reaches on your assumption
On your assumption of 7.00% a year, after 20 years this plan reaches
£161,700.65
Your money compounds at 6.79% a year — the index’s 7.00%, then no currency assumption at all, then 0.20% of charges.
| Invested at the start | £10,000.00 |
|---|---|
| Paid in over the term | £60,000.00 |
| Growth, after charges | £91,700.65 |
| Deducted from the pot | −£0.00 |
| Final value | £161,700.65 |
Nothing is deducted from the pot here, and the zero is not a rounding: charges on this page are modelled as a fund-level ongoing charge, which is taken inside the fund and reaches you as a smaller growth figure instead. The investment fee calculator separates that from a platform fee, which is deducted.
This calculator will not tell you what the S&P 500 has returned. It has no market data, and a figure it invented would be worse than the empty box it asks you to fill in. Every “the index has returned x% a year since 19xx” depends on four choices that are almost never stated — the start date, the end date, whether the figure is in dollars or in pounds, and whether dividends were counted — and moving any one of them moves the answer by percentage points a year. On a forty-year projection that is not a detail; it is most of the answer.
So the rate above is yours, the 7.00% it opens with is a round placeholder rather than a claim about anything, and what this page does instead is answer the two questions that need no market data at all: what return this plan would need, and how far apart the answers are across a range of assumptions. Both are below.
This is not a forecast. It is what would happen if one rate held exactly, every period, for 20 years. Real index returns arrive as a sequence, and the order they arrive in changes the answer — two paths with identical averages can end a long way apart.
What return would this plan need?
To turn this plan into £250,000.00 over 20 years, the index would have to return
10.27%
a year, in dollars, before your 0.20% of annual charges and with no currency movement assumed.
That is the number to have an opinion about. Nobody can tell you what the index will do, but most people can tell whether 10.27% a year for 20 years is something they would plan around — and if it is not, the plan is what needs to change rather than the assumption.
Solved by running the projection repeatedly and narrowing the range, not by rearranging a formula. So the answer agrees with the table below it by construction, including where rounding to whole pence every period makes a closed-form answer disagree.
The same plan across a range of assumptions
| The index returns | After 20 years | Against yours |
|---|---|---|
| 0.00% | £68,417.14 | -£93,283.51 |
| 2.00% | £86,398.93 | -£75,301.72 |
| 4.00% | £110,267.49 | -£51,433.16 |
| 6.00% | £142,040.13 | -£19,660.52 |
| 8.00% | £184,412.23 | £22,711.58 |
| 10.00% | £240,976.61 | £79,275.96 |
| 12.00% | £316,507.03 | £154,806.38 |
The top of that table is 4.6 times the bottom. That ratio is the honest headline of any calculator like this one. It says how much of the answer is the assumption rather than the plan — and it is the thing a page that prints a single figure has quietly hidden from you.
Use the range, not a point. The useful reading is not the middle row; it is whether you would still be all right at the bottom of the table and what you would do differently if you were. A plan that only works at the top of it is a plan that depends on a number nobody can supply, including this page.
It is a dollar index, and you are paid in pounds
| The dollar does | Final value | Against yours |
|---|---|---|
| -4.00% a year | £94,220.51 | -£67,480.14 |
| -2.00% a year | £122,821.28 | -£38,879.37 |
| 0.00% a year — nothing assumed, or fully hedged — yours | £161,700.65 | — |
| 2.00% a year | £214,639.40 | £52,938.75 |
| 4.00% a year | £286,771.29 | £125,070.64 |
A sterling investor in a dollar index holds two positions, not one. The rates compose rather than adding: a 7% index with a 3% weakening of the dollar is (1.07)(0.97) − 1, which is 3.79% and not 4%. Over a long term the compounding of that difference is not a detail.
This is the least defensible assumption on the page, which is why it defaults to nothing. An equity return assumption is at least a claim about something that grows. An exchange rate is a ratio between two economies, and a calculator that asserted a direction for it over twenty years would be making up the one number on this page nobody even pretends to forecast.
Hedged share classes exist, and they are not free. A currency-hedged fund aims to strip the exchange rate out, which is the nought row above. It costs something to do — the amount varies by product and with the gap between the two countries’ interest rates — and this site has no figure for it. Put your own into the charges box and the nought row becomes the hedged answer. This page names no fund and recommends neither choice.
Year by year
| Year | Opening | Paid in | Growth, after charges | Deducted | Closing |
|---|---|---|---|---|---|
| 1 | £10,000.00 | £3,000.00 | £787.77 | £0.00 | £13,787.77 |
| 2 | £13,787.77 | £3,000.00 | £1,044.80 | £0.00 | £17,832.57 |
| 3 | £17,832.57 | £3,000.00 | £1,319.27 | £0.00 | £22,151.84 |
| 4 | £22,151.84 | £3,000.00 | £1,612.41 | £0.00 | £26,764.25 |
| 5 | £26,764.25 | £3,000.00 | £1,925.39 | £0.00 | £31,689.64 |
| 6 | £31,689.64 | £3,000.00 | £2,259.63 | £0.00 | £36,949.27 |
| 7 | £36,949.27 | £3,000.00 | £2,616.55 | £0.00 | £42,565.82 |
| 8 | £42,565.82 | £3,000.00 | £2,997.67 | £0.00 | £48,563.49 |
| 9 | £48,563.49 | £3,000.00 | £3,404.70 | £0.00 | £54,968.19 |
| 10 | £54,968.19 | £3,000.00 | £3,839.30 | £0.00 | £61,807.49 |
| 11 | £61,807.49 | £3,000.00 | £4,303.43 | £0.00 | £69,110.92 |
| 12 | £69,110.92 | £3,000.00 | £4,799.04 | £0.00 | £76,909.96 |
| 13 | £76,909.96 | £3,000.00 | £5,328.29 | £0.00 | £85,238.25 |
| 14 | £85,238.25 | £3,000.00 | £5,893.42 | £0.00 | £94,131.67 |
| 15 | £94,131.67 | £3,000.00 | £6,496.93 | £0.00 | £103,628.60 |
| 16 | £103,628.60 | £3,000.00 | £7,141.41 | £0.00 | £113,770.01 |
| 17 | £113,770.01 | £3,000.00 | £7,829.60 | £0.00 | £124,599.61 |
| 18 | £124,599.61 | £3,000.00 | £8,564.50 | £0.00 | £136,164.11 |
| 19 | £136,164.11 | £3,000.00 | £9,349.27 | £0.00 | £148,513.38 |
| 20 | £148,513.38 | £3,000.00 | £10,187.27 | £0.00 | £161,700.65 |
20 years, rolled up from monthly periods. The CSV export contains every period, not just the year ends.
A worked example you can check
These are the figures the calculator above loads with, so every number in this section can be checked against it without typing anything. £10,000.00 invested, £250.00 a month, over 20 years, with annual charges of 0.20% and no assumption at all about the currency. The 7.00% index return it opens with is a round placeholder chosen to be legible, not a figure this site has looked up — nothing here is a claim about what any index has done.
| Paid in over 20 years, plus the opening amount | £70,000.00 |
|---|---|
| Final value at 7.00% a year | £161,700.65 |
| The same plan at 0.00% a year | £68,417.14 |
| The same plan at 12.00% a year | £316,507.03 |
| The top of that range divided by the bottom | 4.6× |
| The return this plan would need to reach £250,000.00 | 10.27% |
Three things in that table are worth pausing on.
- The range is 4.6 times from bottom to top. Every row uses the same money, the same term and the same charges. The only thing that moves is a number nobody can supply — which means most of the difference between the best and worst answers on this page is not about your plan at all.
- £250,000.00 needs 10.27% a year. That is a question you can answer even though “what will the index return?” is one nobody can. If a rate you would not plan around is what your target requires, the useful change is to the plan rather than to the assumption.
- The currency assumption is nought, and that is a decision. The index is priced in dollars and a sterling investor is exposed to both. Zero asserts nothing, which is the only defensible starting point for an exchange rate over decades — and it is also what a currency-hedged share class aims to deliver, at a cost this site has no figure for.
Methodology: what this calculator does, and what it refuses to do
Why there is no historical return in this tool
Because this site has no market data source, and a figure it invented would be worse than the empty box it asks you to fill in. Every statement of the form “the index has returned x% a year since 19xx” depends on four choices that are almost never printed beside it — the start date, the end date, the currency it is measured in, and whether dividends were counted. Moving any one of them moves the answer by percentage points a year, and over a forty-year projection that is not a detail; it is most of the answer.
So the rate is your assumption, the figure the page opens with is a round placeholder, and no sentence anywhere on this page attributes a return to any index. What the calculator does instead is answer the two questions that need no market data at all: what return this plan would need, and how far apart the answers land across a range of assumptions.
The rate, composed
Two rates go in and one comes out. The index’s dollar return and your currency assumption are composed multiplicatively — (1 + index) × (1 + currency) − 1 — never added: a 7% index with a 3% weakening of the dollar is 3.79%, not 4%. Charges are then applied by the projection engine as a drag on that rate, (1 + r) × (1 − ocf) − 1, and the delivered figure shown on the page is the engine’s own report of what it compounded at rather than a third calculation performed alongside it.
Charges here are one number, modelled as a fund-level ongoing charge. Separating an ongoing charge from a platform fee, an annual cap and a flat fee is a real subject and the investment fee calculator is the page that owns it.
The required return
Solved by running the projection repeatedly and narrowing the range, not by rearranging a formula. A rearranged annuity formula answers a simpler question and then disagrees with the table printed underneath it, which is the failure this whole site is written against. The solver returns the rate at which the target is met, and where no rate in its range reaches the target it says so and by how much — it never hands back the top of its own search range as though it were an answer.
The search is done on the sterling rate, because that is what the projection compounds at, and the answer is converted back to what the index itself would have to do. The range searched is the range this page’s own index field allows, so the answer is always a figure you could type back into the box above.
Currency
The S&P 500 is priced in dollars, so a sterling investor holds two positions: the index and the exchange rate. A strengthening dollar adds to a UK holder’s return and a weakening one takes from it, whatever the index did.
It defaults to nought, deliberately. An equity return assumption is at least a claim about something that grows; an exchange rate is a ratio between two economies with no reason to drift in a particular direction over twenty years. A calculator that asserted one would be inventing the one number on the page that nobody even claims to forecast. A currency-hedged share class aims to remove the exposure — that is the nought row of the table — at a cost that varies by product and that this site has no figure for. Put your own into the charges box.
Conventions, stated
Contributions land at the start of each period, which is what a standing order on payday is. The rate is treated as an effective annual rate, so the figure you type is what a year compounds to — dividing an index’s annual return by twelve and compounding it back would inflate an assumption you never made. Every figure is rounded to whole pence at each period boundary, so every row of the table adds up exactly rather than approximately, at the cost of a pound or two of drift against a textbook formula over a long term.
Sources, and why there is no rates table
Most calculators on this site cite gov.uk, because they implement statutory rates, bands and thresholds that can be checked against a published source. This one has no statutory figures and no market data. There is nothing here an authority could confirm, so the page carries no verification stamp and will not borrow one. Its claim is arithmetic only: given these assumptions and the conventions above, the schedule is what they compound to.
What this is not
It is not a forecast, and it is not a claim about any index, fund or provider. It names none and recommends none — it is information, not advice, and it knows nothing about your circumstances. It does not model tax, ISA or pension allowances, dealing charges or currency conversion charges on each purchase (the ETF calculator models a dealing commission), the difference between a price index and a total return index (the index fund calculator does), or the sequence in which returns arrive — which is the largest thing a constant-rate model leaves out.
Nothing you type here is transmitted or stored — there is no application server and no database. A share link is the exception: it carries your figures in the URL. What that means.
Frequently asked questions
- What return does this calculator assume for the S&P 500?
Whatever you put in the box, and nothing else. This site has no market data source, so it cannot tell you what the index has returned and it will not invent a figure — the 7.00% the page opens with is a round placeholder, not a historical figure, and no sentence on the page attributes it to the index. Every published "the index has returned x% a year" depends on the start date, the end date, the currency and whether dividends were counted, and moving any one of those moves the answer by percentage points a year.
- What return would my plan need to reach my target?
That is the question this page answers instead, and it needs no market data at all. On the defaults — £10,000.00 invested, £250.00 a month for 20 years with 0.20% of annual charges — reaching £250,000.00 needs 10.27% a year from the index. It is solved by running the projection repeatedly and narrowing the range rather than by rearranging a formula, so it agrees with the table beneath it exactly. And it is a number you can have an opinion about, which "what will the index do?" is not.
- How much does the growth assumption change the answer?
Enormously, and that is the most useful thing this page shows. On the defaults the same plan reaches £68,417.14 at 0.00% a year and £316,507.03 at 12.00% — a factor of 4.6, with the money, the term and the charges identical throughout. Any calculator that prints one figure has hidden that from you. The useful reading is whether you would still be all right at the bottom of the range.
- Does the exchange rate matter if I invest in the S&P 500 from the UK?
Yes, and it is not a small effect. The index is priced in dollars, so a sterling investor holds the index and the exchange rate together. The two compose multiplicatively rather than adding: a 7% index with a 3% weakening of the dollar is 3.79%, not 4%. This calculator defaults the currency assumption to nought because an exchange rate is the least defensible thing on the page to assume a direction for over decades — but the table shows what five different assumptions are worth on your own figures.
- What is a currency-hedged fund, and should I use one?
A hedged share class aims to strip the exchange rate out, so the sterling investor gets closer to the index's own return — the "nought" row of the currency table on this page. Hedging costs money to run, the cost varies by product and with the gap between the two countries' interest rates, and this site has no figure for it. If you want to model a hedged class, set the currency assumption to nought and put the higher ongoing charge in the charges box. This page names no fund and recommends neither choice: it is information, not advice.
- Is the S&P 500 figure I see in the news the same one my fund tracks?
Usually not. The level of an index is the price of its constituents and excludes the dividends they pay; a fund holds the shares, receives the dividends and tracks the total return version of the same index. The gap between the two series is roughly the dividend yield, every year, compounded — which is why comparing a statement against a headline index figure is the most common way to conclude wrongly that a tracker is underperforming. The index fund calculator on this site takes that apart, along with the tracking gap and the ongoing charge.
- Is this a forecast of what the S&P 500 will do?
No, and it is not a claim about what it has done either. It computes what would happen if one rate held exactly, every single period, for the whole term — a rate you supplied. Real index returns arrive as a sequence rather than as an average, and the order they arrive in changes the outcome: two paths with identical average returns can end a long way apart, especially once money is being withdrawn. Treat every figure here as arithmetic on an assumption.