Compound Interest Calculator
Estimate savings growth with monthly contributions and monthly compounding. See your projected final balance, total contributions and investment growth.
See how your savings or investment grows over time
How this calculator works
Enter your starting balance, monthly contribution, assumed annual return and time horizon. The estimate separates the money you contribute from the growth generated by compounding.
Interest is compounded monthly at the annual rate divided by 12. Contributions are added at the end of each month, so they begin earning returns in the following month. The assumed return remains constant; actual market returns vary. Taxes, inflation and fees are excluded.
For monthly rate r and n months, the balance is P × (1 + r)ⁿ + C × [(1 + r)ⁿ − 1] ÷ r. P is the starting balance and C is the monthly contribution. At 0%, a $1,000 starting balance plus $100 a month for 10 years totals $13,000.
Common questions
When are contributions added?
At the end of each month, after that month’s interest is calculated.
Does the result predict investment returns?
No. It illustrates a constant return assumption. The actual balance depends on returns, fees, taxes and the timing of contributions.
Related reading: Read the TTN explanation.
Saving for retirement? Use the retirement planning calculator to include spending, inflation and other income.
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TTN Finance · Estimates are for information only and are not financial advice.