Compound Interest Calculator
Compute the future value, total interest and effective annual rate of a savings or investment account with annual / quarterly / monthly / daily / continuous compounding and optional monthly contributions.
Interactive tool
Investment
Result
LiveWhat is a Compound Interest Calculator?
A compound interest calculator computes the future value of an investment when interest is reinvested back into the principal at a chosen frequency. The more often interest compounds, the more dramatically the balance grows over time. This calculator supports six compounding frequencies: annual, semi-annual, quarterly, monthly, daily, and continuous, and lets you stack a regular monthly contribution on top of the initial principal.
How to Use the Compound Interest Calculator
- 1Enter the initial principal and the annual interest rate
- 2Choose the number of years
- 3Pick the compounding frequency that matches your account
- 4Optionally add a regular monthly contribution
- 5Read the future value, total interest earned, and effective annual rate
- 6Compare frequencies in the bottom card to see the impact of compounding faster
Key features
Six compounding frequencies
Annual, semi-annual, quarterly, monthly, daily, continuous
Monthly contribution support
Stack a recurring deposit on top of the initial principal
Effective annual rate (EAR)
Always know what your nominal rate is actually worth
Year-by-year stacked-area chart
See how principal, contributions, and interest grow over time
Frequency comparison panel
Same principal, same rate, different frequencies: side by side
Multi-currency
30+ ISO 4217 currencies for global users
Continuous compounding
Closed-form e^(rt) formula for the theoretical maximum growth
100% private
All calculations run in your browser: no balances or rates leave your device
Why Use a Dedicated Compound Interest Tool?
Spreadsheet formulas treat compounding frequency as a footnote, but the difference between annual and continuous compounding is non-trivial over a 30-year horizon. This tool surfaces all six frequencies at once and adds a contribution-aware year-by-year chart, so you can compare scenarios at a glance.
Common use cases
- Project the value of a high-yield savings account over 10-30 years
- Compare a CD compounding daily vs a money-market compounding monthly
- Plan a child education fund with monthly contributions
- Show the "miracle of compounding" by comparing a $1k deposit at age 25 vs age 35
- Compute the future value of an emergency fund growing at the current Fed rate
- Stress-test a retirement assumption at different return rates
Effective annual rate (EAR)
EAR is what your nominal rate is actually worth after compounding is applied. A 12% nominal rate compounded monthly is equivalent to ~12.68% EAR. Always compare EAR (not nominal) when evaluating savings products.
Continuous compounding intuition
- Continuous compounding is the theoretical limit of "compound it as often as possible"
- It uses the closed-form formula FV = P × e^(r × t)
- It is the upper bound: no real account compounds faster than continuous
- Most banks compound monthly or daily; the gap between daily and continuous is < 0.01%
Why monthly contributions matter
A $100/month contribution over 30 years at 7% grows to over $120,000, even though only $36,000 was deposited. The remaining $84k is pure compounding. This is why "start early" advice for retirement accounts is so persistent.
Tips & best practices
Compare EAR, not nominal
Two accounts can have the same nominal APR but different compounding frequencies. The one with higher EAR is the better deal.
Start early, not big
A small monthly contribution started 10 years earlier almost always beats a larger contribution started later, because the early dollars compound for 10 extra years.
Real returns vs nominal
Subtract long-run inflation (~2-3%) from your rate to see the real (purchasing-power) growth.
Use the comparison panel
The bottom panel makes the impact of compounding frequency obvious: keep it in mind when comparing CDs, savings, and money-market accounts.
Tax is not modelled
Real-world after-tax returns are lower in taxable accounts. Use a tax-equivalent rate, or run the same calculation in a tax-advantaged account scenario.
Privacy & security
This compound interest calculator runs entirely in your browser. No principals, rates, or balances are uploaded, logged, or shared.
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Frequently Asked Questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal; compound interest is calculated on the principal plus accumulated interest. Over long horizons, compound interest produces dramatically larger balances.
How does compounding frequency affect the result?
More frequent compounding produces more interest because each interest payment immediately starts earning its own interest. The order is: continuous > daily > monthly > quarterly > annual. The gap is small for short periods but grows over decades.
What is the effective annual rate (EAR)?
EAR is the actual annual rate of return after compounding is applied. A 12% nominal rate compounded monthly equals ~12.68% EAR. Always compare EAR: not nominal, when shopping savings products.
Does the calculator handle inflation or taxes?
No. It computes pre-tax, nominal returns. To see real (inflation-adjusted) returns, subtract your inflation expectation (~2-3%) from the rate. For after-tax returns in a taxable account, use your marginal tax rate to compute a tax-equivalent rate.
How are monthly contributions modelled?
Contributions are added at the end of each calendar month, then compound at the configured frequency for the rest of the period. This matches how most savings accounts and brokerage auto-deposits work in practice.
Is my data uploaded anywhere?
No. All calculations run entirely in your browser. Principal, rate, and balance values never leave your device.