What your result means
A lump sum projection is the cleanest calculation in investing: one amount, one growth rate, one period. The future value is what the money compounds to; the gains figure is everything above what you put in, and it is the part that may be taxable when you sell.
Because there is only one contribution, the annualised return equals the return you entered minus charges — there is no timing effect to muddy it. That makes a lump sum the fairest way to see what a given return actually does over a given number of years, without a SIP's staggered contributions clouding the picture.
The today's money figure does the real work here. Over fifteen or twenty years, inflation quietly reverses a large share of the apparent gain, and a lump sum invested for a specific future purpose — a deposit, a fee, a retirement — needs to be judged against what that purpose will cost then, not now.
The worst possible day to invest still beats waiting
The fear that stops people investing a lump sum is buying at the peak. It is a reasonable fear and a poor reason to wait: over long horizons the cost of being out of the market has historically been larger than the cost of buying at a bad moment, because the recovery from a bad entry still compounds for decades.
Drip-feeding a lump sum over six or twelve months is a legitimate compromise — not because it produces a better expected outcome, but because it produces one you are more likely to stick with. The calculator will happily show you both: enter the full amount here, or use SIP mode with a shorter term.
How it works
The whole amount is invested in month one and grows at one twelfth of the compounded annual return every month thereafter. No further contributions are added, so the balance curve is a pure exponential — gentle at first and increasingly steep.
Fund charges are deducted monthly from the balance. On a lump sum this is the clearest demonstration of why charges matter: a 1% annual fee on money left alone for twenty years costs roughly 18% of the final value, not 20% of the gain.
If you switch on a tax preset, the tool shows the capital gains tax that would fall due if you sold the entire holding at the end. Nothing is taxed while it stays invested in an accumulating fund.
How to use this calculator
- Enter the lump sum you want to invest.
- Set the expected annual return.
- Set how many years you will leave it invested.
- Open Advanced options for inflation, the fund's ongoing charge, and a UK or India tax preset.
- Read the future value, the today's-money equivalent, and the tax due if you cashed out.
Formula
PV = the amount you invest, r = expected annual return, f = annual charge, n = months invested. Today's money divides the result by (1 + inflation)years.
Worked example
£100,000 invested for 15 years at 10%, with 3% inflation:
Investment gains £317,725
In today's money £268,122
Real return 6.80% a year
Held outside an ISA by a higher-rate UK taxpayer, selling the whole holding at the end would trigger about £75,534 of capital gains tax on that £317,725 gain, after the £3,000 annual exemption. Inside a Stocks & Shares ISA the same holding is free of it — which is why the wrapper is often worth more than the fund choice.
Frequently asked questions
Should I invest it all at once or spread it out?＋
Investing immediately has historically produced the higher expected outcome, because the money spends longer compounding. Spreading it over six to twelve months reduces the chance of a painful entry and is easier to live with. Both are defensible; leaving it in cash indefinitely is the one option the numbers cannot support.
Does this account for capital gains tax?＋
Only if you turn on a tax preset in the advanced options. The tool then shows the tax that would be due if you sold the whole holding at the end of the term — the UK preset applies the £3,000 annual exempt amount and your 18% or 24% rate, and an ISA setting removes it. Gains are not taxed while the money stays invested in an accumulating fund.
Why does a 1% charge cost so much more than 1%?＋
Because you lose the fee and everything that fee would have earned. Over fifteen years at 10%, each pound taken in year one would have become about £4. The charge is 1% a year; the cumulative cost to the final pot is many times that.
Related calculators
Assumptions & limitations
A single-contribution projection still rests on assumptions:
- Returns are assumed constant every year. Real markets are not — they deliver the average through a sequence of good and bad years, and the order those arrive in changes the outcome.
- Growth is compounded monthly from the annual rate you set, so 10% a year becomes 0.797% a month rather than a flat 0.833%.
- Fund charges are deducted monthly from the balance. Platform fees, trading costs and bid-offer spreads are not modelled separately — fold them into the charge figure if you want the full picture.
- Inflation is applied at a single constant rate to produce the "today's money" figures. Your personal inflation rate depends on what you actually buy.
- Nothing here is financial advice, and no projection is a promise. Use it to compare scenarios against each other, not to predict a number.
- Tax, where enabled, is calculated as though the entire holding were sold in one go on the final day, using one year's allowance.