Compound Interest Calculator with Monthly Deposits
Growth with compounding and monthly deposits, year by year.
Use via API
Grow a starting amount with compound interest and optional end-of-month contributions; returns the final balance, interest earned, AER and an optional year-by-year table. Send JSON, get JSON back.
POST https://pithlab.com/api/v1/tools/compound-interest-calculator
curl https://pithlab.com/api/v1/tools/compound-interest-calculator \
-H "Authorization: Bearer $PITHLAB_KEY" \
-H "Content-Type: application/json" \
-d '{"principal":10000,"rate":5,"years":10,"frequency":"monthly","monthlyContribution":200}'About the Compound Interest Calculator
See how savings grow with compound interest. Set the rate, compounding frequency and monthly contributions, then view a year-by-year breakdown.
How to use the Compound Interest Calculator
- Enter your starting amount, the annual interest rate and how many years to grow it for.
- Choose how often interest is compounded and, optionally, a monthly contribution.
- Read the final balance, total paid in and total interest, then check the yearly table or download it as CSV.
Examples
Input
1000, 5%, 10 years, annually
Output
Final balance 1,628.89 (paid in 1,000.00, interest 628.89)
Input
0, 6%, 10 years, monthly, 100/month
Output
Final balance 16,387.93 (paid in 12,000.00, interest 4,387.93)
Frequently asked questions
What formula does this use?
Without contributions, the balance is P × (1 + r/n)^(n × t), where r is the annual rate, n the compounding periods per year and t the years. Monthly contributions are added at the end of each month and earn interest from then on.
How are monthly contributions handled with annual or daily compounding?
Each month the balance grows at the monthly rate equivalent to your chosen compounding, (1 + r/n)^(n/12) − 1. Real accounts may credit interest on mid-period deposits differently, so treat results as estimates.
What is the effective annual rate?
It is the yearly growth once compounding is included, often called AER or APY. 5% compounded monthly is an effective 5.12% a year.
Does this include tax, fees or inflation?
No. It shows nominal growth at a constant rate. Taxes, fees, inflation and changing rates will all affect what you actually end up with.