Compound interest calculator
Work out what a lump sum and a monthly payment grow to in pounds. Set the yearly growth, fees and inflation, and see the value year by year and in today’s money.
- Final value
- £1,110,070
- after 40 years
- Total paid in
- £96,000
- Growth
- £1,014,070
- In today’s money
- £413,424
- after 2.5% inflation a year
Show the figures for each year
| Year | Paid in | Growth | Value |
|---|---|---|---|
| 1 | £2,400 | £108 | £2,508 |
| 2 | £4,800 | £467 | £5,267 |
| 3 | £7,200 | £1,102 | £8,302 |
| 4 | £9,600 | £2,040 | £11,640 |
| 5 | £12,000 | £3,312 | £15,312 |
| 6 | £14,400 | £4,952 | £19,352 |
| 7 | £16,800 | £6,995 | £23,795 |
| 8 | £19,200 | £9,482 | £28,682 |
| 9 | £21,600 | £12,459 | £34,059 |
| 10 | £24,000 | £15,973 | £39,973 |
| 11 | £26,400 | £20,078 | £46,478 |
| 12 | £28,800 | £24,834 | £53,634 |
| 13 | £31,200 | £30,306 | £61,506 |
| 14 | £33,600 | £36,564 | £70,164 |
| 15 | £36,000 | £43,689 | £79,689 |
| 16 | £38,400 | £51,766 | £90,166 |
| 17 | £40,800 | £60,890 | £101,690 |
| 18 | £43,200 | £71,168 | £114,368 |
| 19 | £45,600 | £82,712 | £128,312 |
| 20 | £48,000 | £95,652 | £143,652 |
| 21 | £50,400 | £110,125 | £160,525 |
| 22 | £52,800 | £126,286 | £179,086 |
| 23 | £55,200 | £144,302 | £199,502 |
| 24 | £57,600 | £164,361 | £221,961 |
| 25 | £60,000 | £186,665 | £246,665 |
| 26 | £62,400 | £211,440 | £273,840 |
| 27 | £64,800 | £238,932 | £303,732 |
| 28 | £67,200 | £269,413 | £336,613 |
| 29 | £69,600 | £303,182 | £372,782 |
| 30 | £72,000 | £340,569 | £412,569 |
| 31 | £74,400 | £381,934 | £456,334 |
| 32 | £76,800 | £427,675 | £504,475 |
| 33 | £79,200 | £478,231 | £557,431 |
| 34 | £81,600 | £534,082 | £615,682 |
| 35 | £84,000 | £595,758 | £679,758 |
| 36 | £86,400 | £663,842 | £750,242 |
| 37 | £88,800 | £738,974 | £827,774 |
| 38 | £91,200 | £821,860 | £913,060 |
| 39 | £93,600 | £913,274 | £1,006,874 |
| 40 | £96,000 | £1,014,070 | £1,110,070 |
Growth is added monthly at the yearly rate you enter, and each payment goes in at the end of the month. The fee comes off the growth rate, so 7% with a 1% fee grows at 6%. Your monthly payment stays the same throughout. Today’s money is the final value scaled back by inflation, to show what it would buy at today’s prices. Real returns change from year to year; this uses the same rate every year.
What the results mean
The final value is the pot at the end, before tax. Total paid in is your starting amount plus every monthly payment, and growth is the rest. Growth is interest earning interest: each month’s gain joins the pot, so next month the gain is bigger. That’s why the dark part of each bar gets taller every year while the light part rises in a straight line.
In today’s money shows what the final value would buy at today’s prices. Over 40 years at 2.5% inflation, £1.11 million buys about what £413,000 buys now.
Picking a growth rate
The calculator starts at 10% a year, a bit under the S&P 500’s long-run figure. From 1957 to 2025, with dividends reinvested, it grew 10.7% a year in dollars, before fund charges and tax. That’s an average of very different years: it rose 43.4% in 1958 and fell 37.0% in 2008.
The rate you pick changes the answer a lot. £200 a month for 40 years comes to £296,505 at 5% a year, £494,308 at 7% and £1,110,070 at 10%.
A fund’s yearly fee comes straight off the growth rate, so try 0.1% and 1% to see what a cheaper fund is worth to you. The guide covers tax outside an ISA, the 2008 crash in pounds and dollars, and why starting at 25 rather than 35 adds nearly £700,000 to the pot.