Compound Interest Calculator with Monthly Contributions

See what a starting amount and a regular monthly deposit grow to, with interest separated from what you paid in and a balance for every year.

Runs in your browserFree, no sign-upLast reviewed October 8, 2026

Projection

Final value: 207,241.79
Total invested: 100,000.00
Interest earned: 107,241.79
Growth: 107.2%

Year by year

Year	Invested	Interest	Balance
Year 1	16,000.00	1,096.46	17,096.46
Year 2	22,000.00	2,781.92	24,781.92
Year 3	28,000.00	5,105.27	33,105.27
Year 4	34,000.00	8,119.45	42,119.45
Year 5	40,000.00	11,881.81	51,881.81
Year 6	46,000.00	16,454.44	62,454.44
Year 7	52,000.00	21,904.59	73,904.59
Year 8	58,000.00	28,305.09	86,305.09
Year 9	64,000.00	35,734.84	99,734.84
Year 10	70,000.00	44,279.24	114,279.24
Year 11	76,000.00	54,030.82	130,030.82
Year 12	82,000.00	65,089.78	147,089.78
Year 13	88,000.00	77,564.62	165,564.62
Year 14	94,000.00	91,572.87	185,572.87
Year 15	100,000.00	107,241.79	207,241.79

Rule of 72. At 8% a year, money roughly doubles every 9 years.

Quick answers

How much will 500 a month be worth in 20 years?: At a 7% annual return with monthly compounding, 500 a month grows to 261,982.70 after 20 years. You pay in 120,000 and interest adds 141,982.70. After 30 years the same deposit reaches 613,543.75.
What is the compound interest formula with monthly contributions?: Final value = P x (1 + r/n)^(n x t) + C x (((1 + i)^m - 1) / i) x (1 + i). P is the starting amount, r the annual rate, n compounding periods per year, t years, C the monthly contribution, i the monthly rate (r / 12) and m the number of months.
How long does it take to double money at 8%?: About 9 years. The Rule of 72 says to divide 72 by the annual percentage rate: 72 / 8 = 9. Checked exactly, 10,000 at 8% compounded annually is 19,990.05 after 9 years.
Is daily compounding much better than monthly?: Only slightly. 10,000 at 8% for 10 years reaches 22,196.40 with monthly compounding and 22,253.46 with daily compounding, a difference of 57.06. The gap between annual and monthly compounding is larger, at 607.15.
How much is 10,000 worth after 10 years at 5%?: 16,288.95 with annual compounding, which is 6,288.95 of interest. With monthly compounding it is 16,470.09 and with daily compounding 16,486.65.
Does the calculator adjust for inflation?: No. Every figure is nominal. To see the result in today's money, subtract expected inflation from the return before you calculate. The 8% example falls from 207,241.79 to 155,338.36 when run at 5% to allow for 3% inflation.

About Compound Interest Calculator

Enter a starting amount, a monthly contribution, an annual return and a number of years. The calculator returns the final value, the total you invested, the interest earned and the percentage growth, then lists invested, interest and balance for each year. With 10,000 to start, 500 a month, 8% a year and 15 years of monthly compounding, the final value is 207,241.79: 100,000 paid in and 107,241.79 of interest. Compounding on the starting amount can be annual, half-yearly, quarterly, monthly or daily. Amounts carry no currency symbol, so the figures read the same in dollars, pounds, euros or rupees. Results are nominal: before inflation, tax and fees.

What a monthly contribution grows to at 7% a year

Final value from the calculator with a starting amount of 0, a 7% annual return and monthly compounding. The last column is the total paid in over 30 years.

Monthly contribution	After 10 years	After 20 years	After 30 years	Paid in over 30 years
50	8,704.72	26,198.27	61,354.37	18,000.00
100	17,409.45	52,396.54	122,708.75	36,000.00
200	34,818.89	104,793.08	245,417.50	72,000.00
250	43,523.62	130,991.35	306,771.87	90,000.00
500	87,047.23	261,982.70	613,543.75	180,000.00
1,000	174,094.47	523,965.40	1,227,087.49	360,000.00

Growth on contributions alone is 45.1% after 10 years, 118.3% after 20 and 240.9% after 30, whatever the amount. Time does more than the size of the deposit.

Lump sum growth: 10,000 at 4% to 10% over 10, 20 and 30 years

Final value with no monthly contribution and annual compounding, plus the doubling time from the calculator's Rule of 72 note.

Annual return	10 years	20 years	30 years	Doubles in about
4%	14,802.44	21,911.23	32,433.98	18 years
6%	17,908.48	32,071.35	57,434.91	12 years
8%	21,589.25	46,609.57	100,626.57	9 years
10%	25,937.42	67,275.00	174,494.02	7.2 years

For any other starting amount, scale in proportion: 25,000 gives 2.5 times these figures.

Compounding frequency compared: 10,000 at 8%

The same deposit and rate under each Compounding frequency option. The effective annual rate is the first-year interest as a percentage of the 10,000 deposit.

Compounding frequency	Value after 1 year	Effective annual rate	Value after 10 years
Annually	10,800.00	8.00%	21,589.25
Half-yearly	10,816.00	8.16%	21,911.23
Quarterly	10,824.32	8.24%	22,080.40
Monthly	10,830.00	8.30%	22,196.40
Daily	10,832.78	8.33%	22,253.46

Most of the benefit arrives by monthly compounding. Going from monthly to daily adds 2.78 in the first year on 10,000.

Compound interest formula used for the lump sum and the deposits

Final value = P x (1 + r/n)^(n x t) + C x (((1 + r/12)^(12 x t) - 1) / (r/12)) x (1 + r/12)

P is the Starting amount, r the Annual return as a decimal, n the compounding periods per year from Compounding frequency, t the Years and C the Monthly contribution. The first term grows the starting amount. The second is the future value of a series of monthly payments, and its final factor of (1 + r/12) treats each payment as made at the start of the month. For 10,000 plus 500 a month at 8% for 15 years, the starting amount grows to about 33,069 and the contributions to about 174,173, which add up to the 207,241.79 shown. If the return is 0%, the result is simply everything you paid in.

Worked examples with starting amount and monthly deposit

Default projection

Starting amount 10,000, Monthly contribution 500, Annual return 8%, Years 15, Compounding frequency Monthly

Final value 207,241.79. Total invested 100,000.00. Interest earned 107,241.79. Growth 107.2%.

In the Year by year table, interest (91,572.87) is still below the amount invested (94,000.00) at year 14 and passes it in year 15.

Small start, long horizon

Starting amount 5,000, Monthly contribution 200, Annual return 7%, Years 30, Compounding frequency Monthly

Final value 285,999.99. Total invested 77,000.00. Interest earned 208,999.99. Growth 271.4%.

Larger start, moderate return

Starting amount 25,000, Monthly contribution 300, Annual return 6%, Years 25, Compounding frequency Monthly

Final value 320,561.92. Total invested 115,000.00. Interest earned 205,561.92. Growth 178.7%.

Savings account with daily compounding, no deposits

Starting amount 10,000, Monthly contribution 0, Annual return 4.5%, Years 5, Compounding frequency Daily

Final value 12,523.05. Total invested 10,000.00. Interest earned 2,523.05. Growth 25.2%.

With annual compounding the same deposit reaches 12,461.82, a difference of 61.23 over five years.

Forty years of 100 a month

Starting amount 1,000, Monthly contribution 100, Annual return 10%, Years 40, Compounding frequency Monthly

Final value 691,378.69. Total invested 49,000.00. Interest earned 642,378.69. Growth 1,311%.

A 10% return every year for 40 years is an optimistic assumption. Run a lower rate alongside it.

Assumptions behind the projection

Contributions always compound monthly. The Compounding frequency setting applies to the starting amount only; each monthly deposit earns one twelfth of the annual rate per month whichever option you pick. With 10,000 and 500 a month at 8% for 15 years, switching from Monthly to Annually changes the final value from 207,241.79 to 205,894.26, and all of that difference comes from the starting amount.

Deposits are counted at the start of each month, so the first one earns a full month of interest. If you pay in at the end of the month, your real result will be slightly lower.

The return is fixed for the whole period. Real investments rise and fall from year to year, and a savings rate can change at any time. The contribution is also fixed: there is no option to raise it each year, to make withdrawals, or to deposit weekly or yearly.

The Year by year table shows up to 50 years. The headline figures cover the full period you enter, up to 70 years. Nothing here allows for tax or account charges; to include a fee, subtract it from the Annual return. This is an illustration of the arithmetic, not financial advice.

How to use it

1
Enter the Starting amount you already have, or 0 if you are starting from nothing.
2
Enter the Monthly contribution you plan to add, or 0 for a lump sum left alone.
3
Enter the Annual return as a percentage and the number of Years, from 1 to 70.
4
Choose the Compounding frequency: Annually, Half-yearly, Quarterly, Monthly or Daily.
5
Read Final value, Total invested, Interest earned and Growth in the Projection panel.
6
Scroll the Year by year table for the balance at the end of each year, and check the Rule of 72 note for the doubling time.

Questions people ask

What is compound interest?

Interest that is added to the balance and then earns interest itself. With simple interest, 10,000 at 8% earns 800 every year. With annual compounding it earns 800 in year one, 864 in year two, and more each year after, reaching 21,589.25 after 10 years against 18,000 with simple interest.

What annual return should I enter?

For a savings account, enter the quoted interest rate. For investments there is no guaranteed figure, so test a range, for example 4%, 6% and 8%, and plan around the lower results. Enter the return after fund and platform charges.

What is the difference between Total invested and Final value?

Total invested is your own money: the starting amount plus every monthly contribution. Final value is that plus the Interest earned. Growth is interest as a percentage of the total invested.

How accurate is the Rule of 72?

It is a close estimate for typical rates. At 8% it predicts 9 years, and the exact figure with annual compounding is just over 9 years. It drifts further from the true value at very low or very high rates.

Can I use it for a SIP or a regular savings plan?

Yes. Set Starting amount to 0, put the instalment in Monthly contribution and enter the expected annual return. The calculator assumes each instalment is invested at the start of the month and that the rate is constant.

Can I enter part of a year?

The Years field is designed for whole years from 1 to 70. The Year by year table lists complete years only, so a period such as 7.5 years will not show a row for the final half year.

Why does my bank's figure differ from this result?

Common reasons are a rate that changed during the period, deposits made on a different day of the month, tax deducted from interest, or a day-count method that differs from the one assumed here. Small differences of a fraction of a percent are normal.