Compound Interest Calculator
compound• Project your maturity value from initial deposit, monthly contribution, annual return, and term. • See your assets grow with compounding on a graph.
Work back from a target
Enter the amount you want to reach and see the monthly contribution it takes. Uses the starting amount, rate and period above.
Enter a target to get the monthly contribution and the time it takes.
Value at maturity
106,639,017
Principal 70,000,000 · Gain +36,639,017
Assumes end-of-month contributions and monthly compounding — a pre-tax nominal figure. Taxes, fees, and inflation are not included.
Years for the principal to double
The rule of 72 — divide 72 by the annual return for a quick estimate.
The exact formula is ln2 ÷ ln(1+r). This assumes the principal sits alone with no contributions, and excludes tax and fees.
Frequently asked questions
What is the difference between monthly and annual compounding?
How often the interest is folded back into the principal. Annual compounding does it once a year, monthly does it every month, so the same nominal 7% grows slightly faster monthly (about 7.23% effective). This calculator assumes end-of-month contributions with monthly compounding.
How much do I need to save each month to hit a target?
Enter the figure under Work back from a target and the required monthly amount appears. At 7% over 10 years, reaching 100 million takes about 580,000 a month. Stretch the same target to 20 years and it drops to about 190,000 — time does far more work than the amount does.
What is the rule of 72?
Divide 72 by the annual return and you get roughly how many years it takes to double: 8% gives 72÷8 = 9 years, 6% gives 12. The exact formula is ln2÷ln(1+r), and between 6% and 10% the two differ by about a tenth of a year — close enough for mental arithmetic. The table above shows both.
Are taxes and inflation included?
No. These are pre-tax nominal figures. In practice tax on interest and dividends plus fees come off the top, and inflation erodes what the same amount can buy. With 3% inflation, a 7% nominal return is closer to 4% in real terms.
What annual return should I enter?
There is no single right answer, and past figures do not guarantee future returns. What is certain is that the result grows steeply as you raise the rate, so it is safer to run both a conservative and an optimistic figure and read the outcome as a range rather than a number.