Interest Calculator for Simple and Compound Interest
Calculate simple or compound interest, compare APR vs APY, and see future value and total interest in seconds.
Interest Calculator Inputs
Enter your starting balance, annual rate, time period, and contribution plan to calculate interest.
The calculator returns a future value, total interest earned, and a growth schedule so you can compare scenarios like monthly vs annual compounding or larger vs smaller contributions.
Calculation Type
Simple interest grows linearly on the principal. Compound interest earns interest on interest.
Rate Type
APR is the stated rate before compounding. APY reflects the effective annual rate after compounding.
This is your opening balance before interest or contributions.
Use APR for a nominal rate, or APY if you want compounding included in the annual rate.
You can use decimals for partial years, like 2.5.
Add recurring deposits to see how contributions boost interest growth.
Contribution timing controls when deposits hit your balance. Beginning of period contributions start earning interest earlier than end of period contributions.
Compounding frequency affects how often interest is added to your balance. More frequent compounding can increase total interest, especially over longer time horizons.
Assumptions and How to Use Results
Fixed Rate Assumption
This interest calculator assumes a fixed annual rate over the full time period. If your rate is variable, run multiple scenarios to see a realistic range of outcomes.
No Taxes, Fees, or Inflation
Results show gross interest only. Taxes, fees, and inflation are not included, so treat the output as a clean baseline before real-world adjustments.
APR vs APY in Practice
APR is the nominal rate. APY is the effective annual rate after compounding. If your bank publishes APY, use the APY option to match the advertised yield.
Savings vs Loan Estimates
The calculator is designed for savings and investments. For loans, the estimate may differ from an amortization schedule that includes fees, minimum payments, or changing balances.
Why Use This Interest Calculator?
Plan Savings Growth
Estimate how much your savings or investments can grow with different rates and time horizons.
Test best-case and conservative rates to understand your target balance and timeline.
Compare APR vs APY
See how simple vs compound interest and APR vs APY change your total interest earned.
Switch rate types and compounding frequency to see which account or investment is more competitive.
Track Compounding Impact
Understand how compounding frequency and contributions shape long-term interest growth.
Even small monthly contributions can make a meaningful difference over many years.
Common Interest Questions This Calculator Answers
How much interest will I earn?
Enter your balance, rate, and time period to see total interest earned and your future value. The summary highlights how much growth comes from interest versus contributions.
Does compounding frequency change results?
Yes. Daily, monthly, or annual compounding can produce different totals. This interest calculator shows the impact instantly so you can compare scenarios.
How do contributions affect growth?
Regular contributions increase your principal over time. The calculator lets you choose timing and frequency so you can see how recurring deposits boost compound interest.
What is the difference between simple and compound?
Simple interest grows only on the original principal. Compound interest grows on principal plus previously earned interest, which accelerates growth as time increases.
How should I compare two accounts?
Use the same principal and time period, then switch between APR and APY options and adjust the compounding frequency. The higher future value indicates the stronger yield under equal assumptions.
Why is my APY higher than APR?
APY includes the effect of compounding, so it will be higher than APR at the same stated rate when interest is credited more than once per year.
Example Scenarios to Try
Savings Account Projection
Enter your current balance, APY, and monthly contribution. Compare monthly vs daily compounding to see how much difference frequency makes over several years.
One-Time Investment Growth
Set contributions to zero and compare simple vs compound interest. This shows the difference between linear growth and compounding growth on a single deposit.
Account Rate Comparison
Keep principal and time constant, then switch between APR and APY options or adjust the compounding frequency to find which account produces a higher future value.
Goal Planning Check
Increase years or monthly contributions until the future value meets your target. This gives a quick sense of how much time or savings you need to reach a goal.
How to Use This Interest Calculator
Enter Your Principal
Add the starting balance you plan to save or invest. This is the base amount that earns interest.
Set the Interest Rate
Choose simple or compound interest, then enter APR or APY. If you are using a bank rate, match the rate type shown on your statement.
Choose Time and Frequency
Set years, compounding frequency, and optional contributions to see your future value.
For quick comparisons, change one assumption at a time so you can see which factor matters most.
Key Terms Explained
Principal
The starting balance before interest and contributions. This is the base amount that earns interest.
Interest Rate (APR or APY)
APR is the nominal annual rate. APY is the effective annual rate that includes compounding.
Compounding Frequency
How often interest is added to your balance. More frequent compounding increases total interest over time.
Contribution Timing
Contributions at the beginning of a period earn interest sooner than contributions at the end.
Future Value
The final balance after interest and contributions. This is what your account may be worth at the end.
Total Interest Earned
The difference between your future value and the total amount you invested or contributed.
Interest Calculator FAQ
What is compound interest?
Compound interest means you earn interest on both your principal and previously earned interest, so growth accelerates over time.
When should I use simple interest?
Simple interest is best for quick estimates where interest applies only to the original principal.
Does compounding frequency matter?
Yes. More frequent compounding, like monthly or daily, can increase total interest over long periods.
What is the difference between APR and APY?
APR is the nominal annual rate before compounding. APY is the effective annual rate after compounding is included.
Do regular contributions change results?
Yes. Adding contributions increases your principal over time, which boosts the interest earned, especially with compound interest.
Does this interest calculator include taxes or inflation?
No. Results are based only on your rate, time, and contributions. Taxes, fees, and inflation are not included.
How does contribution timing affect results?
Contributions at the beginning of a period have more time to earn interest than contributions at the end. Over long periods, this difference can be noticeable.
Is this calculator for savings or loans?
It can estimate interest for savings or investments. For loans, results can be a rough estimate, but actual loan schedules may include fees or different amortization rules.
Why is growth vs total invested lower than my rate?
Contributions are added over time, not all at once. Some deposits earn interest for fewer periods, which lowers the overall growth percentage compared to the headline rate.
Can I model withdrawals or changing rates?
This calculator assumes a fixed rate and positive contributions. For withdrawals or variable rates, run multiple scenarios to approximate the range of outcomes.
What does the effective annual rate mean?
It is the annual rate after compounding based on your selected frequency. It helps compare accounts on a like-for-like basis.
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