Compound Interest Calculator
See how an amount grows with compound interest at any rate, time and compounding frequency, with optional monthly deposits and a year-by-year breakdown.
Runs in your browser. Your data is not uploaded.How our tools work
Advanced: monthly deposits
Added at the end of every month.
How do I calculate compound interest?
Compound interest is A = P(1 + r/n)^(nt): the starting amount, times one plus the rate per period, raised to the number of periods. 10,000 at 5% a year for 10 years, compounded annually, grows to 16,288.95, which is 6,288.95 in interest. Enter your numbers, choose the compounding, and optionally add monthly deposits.
- Enter the starting amount, the yearly interest rate and the number of years.
- Choose how often interest is compounded: annually, semi-annually, quarterly, monthly or daily.
- Optionally, add a deposit made at the end of every month under “Advanced”. Read the final balance, the interest and the year-by-year growth.
Want the formula explained step by step, with simple interest for comparison? Read our guide: How Compound Interest Works, With Real Numbers
Formulas & Methods
Compound interest
Example: 5,000 at 4% compounded quarterly for 3 years: 5,000 × (1 + 0.04 ÷ 4)^(4 × 3) = 5,634.13
Monthly deposits
Example: 100 a month at 6% compounded monthly for a year = 1,233.56
Key features
Any compounding
Annual, semi-annual, quarterly, monthly or daily (365 times a year).
Monthly deposits
Add a regular deposit at the end of each month, calculated exactly for the compounding you choose.
Year-by-year table
See the balance, deposits and interest at the end of every year.
Effective yearly rate
See what the compounding is worth as one yearly rate: 5% compounded monthly works out at 5.12% a year.
Why compounding frequency matters
With compounding, interest earns interest. The more often it is added, the faster the balance grows: 10,000 at 5% for 10 years becomes 16,288.95 compounded annually, 16,436.19 quarterly and 16,470.09 monthly.
The effective yearly rate shows the same thing as one number: 5% a year compounded quarterly is worth 5.09% a year, and compounded monthly 5.12%. Use it to compare offers that compound differently.
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Frequently Asked Questions
How long does money take to double?
For a quick estimate, divide 72 by the yearly rate: at 5% that is about 14.4 years. With yearly compounding the exact answer is 14.2 years, from t = log 2 ÷ log 1.05.
When are the monthly deposits added?
At the end of each month. Money deposited earlier would earn slightly more.
What does daily compounding use?
365 compoundings a year. Some banks use 360; the difference is very small.
Is this a guaranteed return?
No. It assumes the rate stays the same for the whole period. Real rates change, and investments can lose value.
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Related guides & tutorials
How Compound Interest Works, With Real Numbers
The compound interest formula explained with worked examples, the effect of compounding frequency, simple vs compound interest, deposits and the rule of 72.
The EMI Formula Worked Out by Hand, With a Spreadsheet Version
The EMI formula step by step, with worked loan examples, total interest and repayment, how rate and tenure change the cost, and flat vs reducing rates.