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Compound interest calculator

See how savings or an investment grow with compound interest and regular contributions, year by year, with inflation and compounding options.

Future value$144,572.72After 20 yrs · 7.229% APY
Total deposits$58,000
Total interest$86,573

Growth by year

Year-by-year

Year-by-year growth
YearDepositsInterestTotal depositsTotal interestBalance
1$2,400.00$801.42$12,400.00$801.42$13,201.42
2$2,400.00$1,032.85$14,800.00$1,834.27$16,634.27
3$2,400.00$1,281.01$17,200.00$3,115.28$20,315.28
4$2,400.00$1,547.11$19,600.00$4,662.39$24,262.39
5$2,400.00$1,832.45$22,000.00$6,494.83$28,494.83
6$2,400.00$2,138.41$24,400.00$8,633.24$33,033.24
7$2,400.00$2,466.49$26,800.00$11,099.74$37,899.74
8$2,400.00$2,818.29$29,200.00$13,918.03$43,118.03
9$2,400.00$3,195.52$31,600.00$17,113.55$48,713.55
10$2,400.00$3,600.02$34,000.00$20,713.58$54,713.58
11$2,400.00$4,033.77$36,400.00$24,747.34$61,147.34
12$2,400.00$4,498.86$38,800.00$29,246.20$68,046.20
13$2,400.00$4,997.58$41,200.00$34,243.79$75,443.79
14$2,400.00$5,532.35$43,600.00$39,776.14$83,376.14
15$2,400.00$6,105.79$46,000.00$45,881.93$91,881.93
16$2,400.00$6,720.67$48,400.00$52,602.60$101,002.60
17$2,400.00$7,380.00$50,800.00$59,982.60$110,782.60
18$2,400.00$8,087.00$53,200.00$68,069.60$121,269.60
19$2,400.00$8,845.11$55,600.00$76,914.70$132,514.70
20$2,400.00$9,658.02$58,000.00$86,572.72$144,572.72
How we calculate

Without contributions, compound interest follows:

A = P × (1 + r/m)^(m·t)
P = initial deposit, r = annual rate, m = compounding periods per year, t = years. Continuous compounding: A = P·e^(rt).

With regular contributions, each deposit grows for the time it is invested. We step through every month using the rate equivalent to your compounding for that period, so different compounding and contribution schedules combine exactly:

i = (1 + r/m)^(m/p) − 1
p = 12 contributions per year

For you: i = 0.583333% per month. Each month the balance is multiplied by (1 + i) and your contribution is added after interest is credited. The effective annual yield is 7.229%.

Rule of 72: money doubles in about 72 ÷ 7 = 10.3 years; the exact figure at this compounding is 9.9 years.

Runs in your browser · no uploadHow it works

How to use Compound interest calculator

  1. 1

    Enter what you start with

    Type the initial deposit and the amount you'll add regularly, then choose how often and whether it goes in at the start or end of each period.

  2. 2

    Set rate, compounding and time

    Add the expected annual rate, pick how often interest compounds, and enter the number of years and months.

  3. 3

    Read the growth

    See the future value, deposits versus interest, the yearly chart and table; switch on inflation or tax for a more conservative view.

  4. 4

    Or work back from a goal

    Choose Reach a goal, enter a target and solve for the time needed or the contribution required.

Limits and Pro

Free and unlimited: durations up to 100 years (150 years when solving for time), rates from −50% to 100%, any currency, and CSV export of the yearly table.

About Compound interest calculator

This calculator projects a savings account, index fund or retirement pot forward in time. You get the future value, how much of it you deposited, how much is interest, an end-of-year chart that stacks your initial deposit, contributions and earned interest, and a table you can download as CSV.

Contributions can be weekly, every two weeks, monthly, quarterly, twice a year or yearly, made at the start or end of each period, and can rise by a percentage every year to mimic pay increases. Interest can compound daily, weekly, monthly, quarterly, semi-annually, annually or continuously; the two schedules are combined with the exact equivalent rate per contribution period rather than an approximation. Optional switches show the result in today's money after inflation and after a flat tax on gains.

Goal mode turns the question around: enter a target and see either how long it takes or how much you need to put away each period to get there by a chosen date.

Typical uses are checking whether a monthly savings habit reaches a house deposit, comparing a high-yield account's APY with a bond, or showing a teenager what starting ten years earlier is worth. Returns on real investments vary from year to year, while this model applies one steady rate; fees, changing tax rules and withdrawals are not modelled, so use it to compare scenarios rather than to predict an exact balance.

Privacy

All projections are computed in your browser — no figures, goals or currency choices are sent to a server. The inputs are stored in the page link and in this browser's local storage so the scenario is still there when you come back.

Features

Stacked yearly chart

Initial deposit, contributions and interest per year, with exact values on hover or keyboard focus.

Goal solver

Time to reach a target, or the exact contribution needed to reach it by a date.

Inflation and tax views

See the future balance in today's money and after a simple tax on gains.

Compound interest calculator: frequently asked questions

How much will $10,000 grow in 10 years at 5%?
Compounded once a year it becomes $16,288.95. Monthly compounding gives $16,470.09, daily $16,486.65 and continuous $16,487.21, so moving from annual to daily compounding adds about $198 over the decade. Adding $100 at the end of every month as well, with monthly compounding, takes the total to $31,998.32 — $22,000 deposited and almost $10,000 of interest.
How much must I save each month to reach $1 million?
Starting from zero at a steady 7% a year compounded monthly, you need about $820 a month for 30 years, $1,920 a month for 20 years, or only $381 a month for 40 years. Time matters more than the amount: ten extra years cut the monthly requirement by more than half. Use Reach a goal with your own rate and starting balance for a precise figure.
What is the difference between APR and APY?
APR is the nominal yearly rate before compounding; APY, also called the effective annual rate, includes the effect of compounding within the year. A 5% rate compounded monthly has an APY of 5.116%, and compounded daily 5.127%. Banks advertise savings accounts by APY because it is the higher number, so compare accounts on APY and enter APR with its matching compounding here.
Does it matter if I contribute at the start or end of the month?
Yes, a little. Money deposited at the start of a period earns one extra period of interest. Saving $100 a month for 10 years at 5% compounded monthly produces $15,528.23 when you pay at the end of each month and $15,592.93 when you pay at the start — about $65 more. The gap widens with higher rates and longer horizons.
What is the rule of 72?
It is a shortcut for doubling time: divide 72 by the annual rate in percent. At 7% money doubles in about 72 ÷ 7 ≈ 10.3 years; the exact figure with annual compounding is 10.24 years. It works best for rates between about 4% and 12%. The formula panel shows both the rule-of-72 estimate and the exact doubling time for your inputs.

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