See how a starting amount plus a regular monthly addition grows when the returns are reinvested. Updated 7 Nov 2026.
Compound interest means earning returns on your returns. Each year the gain is added to the amount invested, so the next year's gain is worked out on a bigger base. Over short periods the effect is small; over decades it does most of the work. Albert Einstein may never have called it the eighth wonder of the world, but the arithmetic is real: at 15% a year money roughly doubles every five years, so Rs 1 becomes about Rs 16 in twenty years.
For a single amount: A = P × (1 + r / n)n × t, where P is the starting amount, r the yearly rate, n the number of compounding periods a year (12 for monthly, 1 for yearly) and t the number of years. The calculator above also adds a fixed amount every month and shows the value year by year.
Starting with Rs 500,000 and adding Rs 10,000 every month at 15% a year, compounded monthly, grows to about Rs 49.72 lakh after 10 years from Rs 17.00 lakh of your own money. The table shows how the gap between what you put in and what you end with widens over time.
| Period | You put in | Value at 15% a year | Money multiple |
|---|---|---|---|
| 5 years | Rs 11.00 lakh | Rs 19.39 lakh | 1.8x |
| 10 years | Rs 17.00 lakh | Rs 49.72 lakh | 2.9x |
| 15 years | Rs 23.00 lakh | Rs 1.14 crore | 4.9x |
| 20 years | Rs 29.00 lakh | Rs 2.48 crore | 8.6x |
| 25 years | Rs 35.00 lakh | Rs 5.32 crore | 15.2x |
| 30 years | Rs 41.00 lakh | Rs 11.30 crore | 27.6x |
A quick way to estimate doubling time: divide 72 by the yearly return. At 12% money doubles in about 6 years, at 18% in about 4, at 9% in about 8. The same rule works for inflation: at 9% inflation, prices double in about 8 years, which is why the real (after-inflation) return matters.
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Simple interest is paid only on the original amount. Compound interest is also paid on the interest already earned, so the balance grows faster every year.
Some. Rs 100,000 at 15% for 10 years grows to about Rs 4.44 lakh with monthly compounding and Rs 4.05 lakh with yearly compounding.
About 5 years (72 / 15 = 4.8). The exact figure is 4.96 years with yearly compounding.
Yes, when dividends are reinvested and the companies keep growing their profits. Unlike a bank deposit, the return is not fixed and the value can fall.
At 15% a year for 10 years, compounded monthly, the total grows to about Rs 49.72 lakh from Rs 17.00 lakh invested.