See what your money grows into with regular contributions, how much to put in to reach a goal, and how long it takes. Everything is calculated in your browser.
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Future value$106,639
You put in$70,000
Interest earned$36,639
Compounding added$8,814versus simple interest on the same contributions
Balance by yearContributionsInterest
Year 10 · contributions $70,000 · interest $36,639 · $106,639
▾Year-by-year and monthly table
Year
Put in
Interest
Balance
1
$16,000
$919.19
$16,919
2
$22,000
$2,339
$24,339
3
$28,000
$4,294
$32,294
4
$34,000
$6,825
$40,825
5
$40,000
$9,973
$49,973
6
$46,000
$13,782
$59,782
7
$52,000
$18,299
$70,299
8
$58,000
$23,578
$81,578
9
$64,000
$29,671
$93,671
10
$70,000
$36,639
$106,639
Interest accrues monthly; contributions are added at the end of each period. Taxes and fees are not included.
How to use it
Future value — enter the starting amount, contribution, time and rate to get the final balance, total contributions and interest earned.
Contribution for a goal — enter the goal and the time; the calculator finds how much to contribute each month, quarter or year.
Time to reach a goal — enter the goal and the contribution to see how many years and months it takes.
The default example: $10,000 to start and $500 every month for 10 years at 7% compounded monthly. The result is $106,639: $70,000 of your own money and $36,639 of interest. With simple interest it would be $97,825 — $8,814 less.
The compound interest formula
A = P × (1 + r / n)n × t
A is the final amount, P the starting amount, r the annual rate as a decimal (7% = 0.07), n the number of compounding periods per year and t the time in years. Regular contributions add a second term — the contributions with the interest they have earned:
A = P × (1 + i)m + C × ((1 + i)m − 1) / i
Here i is the rate per period (r / 12 for monthly compounding), m the number of periods and C the contribution made at the end of each period. The calculator steps through the months one by one, so it also handles what the formula does not: quarterly contributions with monthly compounding, a term in months, or interest that is not reinvested.
Simple vs. compound interest
$10,000 at 7% with no contributions. Simple interest pays the same $700 every year; compound interest (monthly) grows with the balance.
Time
Simple interest
Compound interest
Difference
1 year
$10,700
$10,723
$23
5 years
$13,500
$14,176
$676
10 years
$17,000
$20,097
$3,097
20 years
$24,000
$40,387
$16,387
30 years
$31,000
$81,165
$50,165
Compounding in stocks: reinvested dividends
A savings account compounds by adding interest to the balance. With stocks the same job is done by reinvesting dividends: each payout buys more shares, and the next payout arrives on a larger number of them. Unlike a deposit rate, dividends are not fixed — companies raise, cut and skip them, and the share price moves. The dividend calculator projects this year by year from a company’s actual dividend per share in its SEC filings; what a company earns before it pays anything out is in its earnings report charts.
Frequently asked questions
What is compound interest?
Interest earned on interest. Instead of being paid out, each period's interest is added to the balance, and the next period's interest is calculated on the larger amount. Example: $10,000 at 7% compounded monthly becomes $20,097 in 10 years; with simple interest it would be $17,000.
What is the compound interest formula?
A = P × (1 + r / n)^(n × t), where P is the starting amount, r the annual rate as a decimal, n the number of compounding periods per year and t the time in years. With regular contributions C at the end of each period, add C × ((1 + i)^m − 1) / i, where i is the rate per period and m the number of periods.
How often should interest compound?
More often is better, but the gain shrinks quickly. At a 7% nominal rate the effective annual rate is 7.00% with annual compounding, 7.19% quarterly, 7.23% monthly and 7.25% daily.
How much do I need to save each month to reach $1 million?
It depends on the time and the rate. Starting from zero at 7% compounded monthly: about $820 a month over 30 years, or about $1,920 a month over 20 years. Use the “Contribution for a goal” mode for your own numbers.
What is the Rule of 72?
A shortcut for doubling time: divide 72 by the annual rate in percent. At 7% that is 72 ÷ 7 ≈ 10.3 years; counting month by month with monthly compounding, the balance passes double after 10 years. The rule works best for rates between roughly 4% and 20%.
Does the calculator include taxes and inflation?
Inflation — yes: fill in the inflation field and the result is also shown in today's money. Taxes and fees — no: they depend on the account and the investment. To approximate them, lower the rate.
Is 7% a realistic rate of return?
It is only an example. The calculator applies one constant rate every year; real returns on stocks vary widely from year to year and can be negative, and a savings account pays whatever its bank currently offers. Try several rates to see how sensitive the result is.