Compound interest calculator
See how savings grow when interest earns interest, with an optional amount added each month.
Results
Balance after 10 years
$54,713.58
This is what your starting amount and monthly additions grow to in 10 years at 7% a year, with interest added every month.
- Total you put in
- $34,000.00Starting amount plus monthly additions
- Interest earned
- $20,713.58
- Actual yearly growth
- 7.23%What the rate adds up to in a year, once interest also earns interest
What you put in and interest earned
Saving and PDF download use a free account. Everything else works without one.
How it works
Compounding means interest is added to your balance and then earns interest itself. We grow the balance month by month using the monthly rate that matches how often interest is added, so money added part-way through a period earns its fair share. The actual yearly growth shows what the stated rate is really worth once interest also earns interest.
Formula
- n = compounding periods per year, r = yearly rate ÷ 100
- Monthly rate i = (1 + r ÷ n)^(n ÷ 12) − 1
- Each month: balance = balance × (1 + i) + amount added
- Actual yearly growth = (1 + r ÷ n)^n − 1
Frequently asked questions
Does adding interest more often make a big difference?
It helps, but less than most people expect. Moving from yearly to monthly compounding at 6% lifts the actual yearly growth from 6% to about 6.17%. The rate itself and the time you stay invested matter far more.
Why does the money I add each month earn interest if interest is added yearly?
We use the monthly rate that grows to exactly the same amount over a full year or other period between interest payments. That way money added mid-period earns a proportional share of interest instead of none at all. Some banks only credit interest on balances held for a full period, so their figures can be slightly lower.
Is this the same as an investment return?
The maths is the same, but investments rarely grow at a steady rate. Use a cautious long-run average and remember that real returns rise and fall from year to year.
Does this include tax or inflation?
No. Interest may be taxed where you live, and inflation reduces what the final amount can buy. The inflation calculator can show what a future sum is worth in today's money.
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Results are estimates only, not financial advice. Read the disclaimer.