Interest Calculator
Calculate simple or compound interest on any principal amount. Enter your starting balance, annual interest rate, time period, and compounding frequency to instantly see your total interest earned, final balance, and a complete year-by-year breakdown.
Initial deposit or loan amount
e.g. 5 for 5% per year
1–50 years
How often interest compounds
Principal
$10,000.00
Interest Earned
$6,288.95
Final Balance
$16,288.95
Principal vs. Interest Breakdown
Year-by-Year Breakdown
| Year | Starting Balance | Interest Earned | Ending Balance | Total Interest |
|---|---|---|---|---|
| 1 | $10,000.00 | $500.00 | $10,500.00 | $500.00 |
| 2 | $10,500.00 | $525.00 | $11,025.00 | $1,025.00 |
| 3 | $11,025.00 | $551.25 | $11,576.25 | $1,576.25 |
| 4 | $11,576.25 | $578.81 | $12,155.06 | $2,155.06 |
| 5 | $12,155.06 | $607.76 | $12,762.82 | $2,762.82 |
| 6 | $12,762.82 | $638.14 | $13,400.96 | $3,400.96 |
| 7 | $13,400.96 | $670.04 | $14,071.00 | $4,071.00 |
| 8 | $14,071.00 | $703.55 | $14,774.55 | $4,774.55 |
| 9 | $14,774.55 | $738.73 | $15,513.28 | $5,513.28 |
| 10 | $15,513.28 | $775.67 | $16,288.95 | $6,288.95 |
Results are estimates for informational purposes only and do not constitute financial or investment advice. Actual returns vary based on compounding terms, taxes, fees, and other factors. Consult a qualified financial professional before making any investment or savings decisions.
How to Use This Interest Calculator
This calculator supports both simple and compound interest. Follow these steps to get your result:
- Choose interest type — select Compound for savings accounts, investments, and most loans, or Simple for straightforward interest calculations without reinvestment.
- Enter the principal — the initial amount you are depositing or borrowing.
- Enter the annual interest rate — the percentage rate per year. Use your savings account APY, loan rate, or estimated investment return.
- Set the time period — enter the number of years (1–50) you want to calculate for.
- Select compound frequency (compound mode only) — choose how often interest is added to your balance: annually, semi-annually, quarterly, monthly, or daily. More frequent compounding means slightly higher returns.
Results update instantly as you type. The year-by-year table shows your starting balance, interest earned, and ending balance for every year of the period.
Interest Formulas
Compound Interest
A = P(1 + r/n)^(n × t)- A = Final amount
- P = Principal
- r = Annual rate (decimal)
- n = Compounds per year
- t = Time in years
Example: $10,000 at 5% compounded annually for 10 years → $16,288.95
Simple Interest
A = P × (1 + r × t)- A = Final amount
- P = Principal
- r = Annual rate (decimal)
- t = Time in years
Example: $10,000 at 5% simple for 10 years → $15,000.00
Compounding Frequency Reference
| Frequency | Times per year (n) | $10,000 at 5% for 10 yrs |
|---|---|---|
| Annually | 1 | $16,288.95 |
| Semi-annually | 2 | $16,386.16 |
| Quarterly | 4 | $16,436.19 |
| Monthly | 12 | $16,470.09 |
| Daily | 365 | $16,486.65 |
More frequent compounding increases the final balance, but the difference diminishes as frequency increases — monthly vs. daily is far less impactful than annually vs. monthly.
Frequently Asked Questions
Simple interest is calculated only on the original principal — the amount you start with — so the same dollar amount is added each year. Compound interest is calculated on the principal plus any previously accumulated interest, meaning interest earns interest and growth accelerates over time. For long time horizons, compound interest can produce dramatically higher final balances.
Compounding frequency is how often accumulated interest is added back to your balance within a year. 'Monthly' means interest is calculated and added 12 times per year; 'daily' means 365 times. More frequent compounding produces slightly higher returns because interest starts earning interest sooner. The difference grows more significant as the rate and time period increase.
The compound interest formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal (e.g. 5% = 0.05), n is the number of times interest compounds per year, and t is the time in years. The total interest earned is A − P.
Simple interest is calculated as I = P × r × t, where P is the principal, r is the annual interest rate as a decimal, and t is the time in years. The final amount is A = P + I. Because there is no compounding, the interest earned each year is always the same flat amount.
The Rule of 72 is a quick mental shortcut to estimate how long it takes for an investment to double at a given compound interest rate. Divide 72 by the annual interest rate percentage. For example, at 6% per year, your money doubles in approximately 72 ÷ 6 = 12 years. It is most accurate for rates between 4% and 12%.
No — this calculator computes gross interest growth only, without deducting taxes on interest income or adjusting for inflation. In practice, interest earned in a taxable account is typically subject to income tax, and inflation erodes purchasing power over time. For a realistic picture of long-term savings, subtract your marginal tax rate from the effective return and consider using a real (inflation-adjusted) rate.
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