7 min read
2026-03-03
Albert Einstein called compound interest “the eighth wonder of the world.” What is his strength?
With simple interest, income is accrued only on the initial amount. In case of complex payments – for the amount plus all previous accruals.
Invest 100,000 rubles at 12% per annum:
| Year | Simple % | Complex % |
|---|---|---|
| 1 | 112,000 | 112,000 |
| 5 | 160,000 | 176 234 |
| 10 | 220,000 | 310 585 |
| 20 | 340,000 | 964 629 |
| 30 | 460,000 | 2,995,992 |
Over 30 years, the difference is almost 2.5 million rubles!
A simple formula for estimating the time to double your capital:
**Number of years = 72 / interest rate**
At 6% per annum: 72 / 6 = **12 years**
At 12% per annum: 72 / 12 = **6 years**
At 18% per annum: 72 / 18 = **4 years**
It is more profitable to start investing at 25 than at 35, even with smaller amounts. 10 years of additional growth can double your total capital.
A difference of 2–3% seems small, but over a horizon of 20–30 years it leads to a multiple difference in results.
Monthly replenishment accelerates growth by averaging the purchase price.
Compound Interest Calculator allows you to set the initial amount, interest rate, term and regular payments - and instantly see the final result.
See also: Investment calculator, Pension calculator, Deposit calculator