Compound Interest Calculator
See how money you already have could grow when interest is repeatedly added to the balance and earns interest itself.
Calculate compound growth
See what changes
Adjust an assumption below without changing your original calculation.
Interest earned in this scenario: —
Amounts are rounded to the nearest whole currency unit for display.
Year-by-year illustration
| Year | Balance | Total interest |
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Compound interest formula and how to calculate it
The standard compound interest formula is A = P(1 + r/n)nt, where A is the ending balance, P is the starting principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years.
To calculate compound interest, subtract the starting principal from the ending balance. For example, if $10,000 grows to $19,671, the compound interest earned is $9,671.
What is compound interest?
Compound interest means interest is calculated on the original principal and on interest previously added to the balance. Over longer periods, that compounding can make the growth path increasingly different from simple interest.
What this calculator includes
This calculator models one starting lump sum. It does not include recurring monthly contributions. If you plan to keep adding money, use our investment growth calculator instead.
Why compounding frequency matters
With the same stated annual rate, more frequent compounding can slightly increase the ending balance because interest is credited more often. The effect depends on the rate and time horizon.
What the result does not predict
The calculation assumes the entered rate remains constant. Real investment returns can vary and can be negative. Bank products may use different rate conventions, fees or calculation methods.
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How Much Will My Money Grow? includes ongoing monthly contributions. Reach $1 Million works backward from a future target.