Compound interest calculator
How a lump sum and monthly deposits grow at a fixed annual return — in money of the day and after inflation.
At this return money doubles roughly every 11.9 years; the rule of 72 gives a similar figure.
Balance at the end of each year
Year by year
| Year | Balance | Paid in | Growth | Today's money |
|---|---|---|---|---|
| 1 | €16,763.26 | €16,000.00 | €763.26 | €16,434.57 |
| 2 | €23,932.32 | €22,000.00 | €1,932.32 | €23,003.00 |
| 3 | €31,531.53 | €28,000.00 | €3,531.53 | €29,712.86 |
| 4 | €39,586.68 | €34,000.00 | €5,586.68 | €36,571.98 |
| 5 | €48,125.15 | €40,000.00 | €8,125.15 | €43,588.43 |
| 6 | €57,175.92 | €46,000.00 | €11,175.92 | €50,770.58 |
| 7 | €66,769.74 | €52,000.00 | €14,769.74 | €58,127.08 |
| 8 | €76,939.19 | €58,000.00 | €18,939.19 | €65,666.86 |
| 9 | €87,718.81 | €64,000.00 | €23,718.81 | €73,399.17 |
| 10 | €99,145.20 | €70,000.00 | €29,145.20 | €81,333.59 |
| 11 | €111,257 | €76,000.00 | €35,257.17 | €89,480.03 |
| 12 | €124,096 | €82,000.00 | €42,095.87 | €97,848.75 |
| 13 | €137,705 | €88,000.00 | €49,704.89 | €106,450 |
| 14 | €152,130 | €94,000.00 | €58,130.44 | €115,296 |
| 15 | €167,422 | €100,000 | €67,421.53 | €124,397 |
| 16 | €183,630 | €106,000 | €77,630.09 | €133,765 |
| 17 | €200,811 | €112,000 | €88,811.16 | €143,412 |
| 18 | €219,023 | €118,000 | €101,023 | €153,351 |
| 19 | €238,328 | €124,000 | €114,328 | €163,595 |
| 20 | €258,791 | €130,000 | €128,791 | €174,159 |
Deposits at the end of each month; the annual return is applied as its monthly equivalent; no taxes or fees.
How the calculation works
Each month the balance earns the monthly equivalent of the annual return, (1 + r)^(1/12) − 1, and then the deposit is added. Over a full year a lump sum therefore grows by exactly the annual rate.
The figure in today's money divides the result by (1 + inflation)^years, so you can compare it with today's prices. Taxes, fund fees and currency moves are not included — subtract them from the return if they apply to you.
Real returns are not smooth: markets sometimes fall 20–50 %, and a fixed rate hides that. The FIRE and mortgage calculators show a range of outcomes instead of one line.
Questions and answers
What return should I use?
There is no right number. Long-run world equity returns have been around 5–7 % a year before inflation and bonds a few percent; future returns can be lower. Try a cautious and an optimistic value and plan with the cautious one.
What is the rule of 72?
Dividing 72 by the annual return in percent gives the approximate years to double: at 6 % about 12 years. The calculator shows the exact figure, ln 2 ÷ ln(1 + r).
Why does starting early matter so much?
Because growth compounds on earlier growth: late in a long horizon the balance gains more from returns than from deposits. The year-by-year table shows when growth overtakes what you paid in.
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