Interest Calculator
Calculate compound interest with optional monthly contributions over any period. This free online financial calculator runs entirely in your browser — no signup, no data sent anywhere.
Inputs
Results
Interactive Chart
Drag to pan, scroll to zoom, shift+drag to box-zoom. Combined view of balance, principal paid, interest paid, and total paid.
Amortization Schedule
| Period | Payment | Principal | Interest | Balance |
|---|---|---|---|---|
| Click Calculate to generate the schedule. | ||||
How It Works (Formula & Method)
Future value of a single deposit compounds as FV = P × (1 + r/n)^(n×t). Recurring contributions are summed as an annuity, also compounding at the same periodic rate. This calculator runs the math month-by-month (or whatever compounding frequency you choose) and plots the trajectory.
Worked Example
Scenario: $10,000 starting deposit, no monthly contributions, 5% annual rate, compounded monthly for 10 years.
- Periodic rate = 5% ÷ 12 ≈ 0.4167%/month.
- Number of periods = 10 × 12 = 120 months.
- Future value = $10,000 × (1.004167)¹²⁰ ≈ $16,470.09.
- Interest earned = $16,470.09 − $10,000 = $6,470.09 — about 64.7% growth from the starting balance.
If you instead added $100/month, the future value would jump to roughly $32,000 — most of the extra coming from the contributions themselves, but a meaningful chunk from compounding on those contributions.
About the Interest Calculator
Compound interest is the interest you earn on top of interest already earned. It is why long-term savings, retirement accounts, and reinvested dividends grow so dramatically — small differences in rate or time compound into very large differences in final value.
Frequently Asked Questions
What compounding frequency should I use?
Most U.S. savings accounts and CDs compound monthly or daily. Use whatever your account discloses; the difference between monthly and daily is small.
What does the Interest Calculator compute?
The Interest Calculator takes 5 input values and returns 3 results. Calculate compound interest with optional monthly contributions over any period.
Is my data sent to a server?
No. The Interest Calculator runs entirely in your browser using static JavaScript. Your inputs are never transmitted to CalculatorHive or any third party, and nothing is stored after you close the page.
Is this calculator free to use?
Yes. Every calculator on CalculatorHive is completely free. There is no signup, no paywall, and no usage limit. The site is supported by display advertising and affiliate partnerships, which are clearly labeled.
Reviewed against: IRS publications, Consumer Financial Protection Bureau (consumerfinance.gov), and current published market data. Results are estimates for educational use only — not financial, tax, or legal advice.