Interest Calculator
Work out the interest on any amount two ways at once, simple and compound, with the formula shown. You can also solve for the interest rate, time or deposit needed to reach a goal, and count interest by the day between two dates.
Interest calculator
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Interest between two dates
Simple interest by the day, the way banks figure interest on a CD that closes early, a private loan between family members or a late payment.
Simple vs compound interest
Simple interest is paid only on the original amount: I = P × r × t. $10,000 at 5% for 3 years earns $1,500. Car loans, many personal loans and Treasury bills use simple interest.
Compound interest is also paid on interest already earned: A = P × (1 + r/n)nt. The same $10,000 at 5% compounded monthly for 3 years earns $1,614.72. Savings accounts, CDs and credit cards compound.
| Years | Simple interest on $10,000 at 5% | Compound (monthly) |
|---|---|---|
| 1 | $500 | $512 |
| 5 | $2,500 | $2,834 |
| 10 | $5,000 | $6,470 |
| 20 | $10,000 | $17,126 |
| 30 | $15,000 | $34,677 |
For regular monthly deposits and a year-by-year table, use the compound interest calculator. For loan payments, use the loan calculator.
Common questions
How do I calculate interest?
For simple interest multiply principal × annual rate × years: $10,000 × 5% × 3 = $1,500. For compound interest use P × (1 + r/n)^(nt) − P.
How much interest will $10,000 earn in a year?
At 5% simple interest, $500. Compounded monthly, $511.62, because each month's interest earns interest too.
How do I calculate interest per day?
Multiply the balance by the annual rate and divide by 365 (or 360 for some loans). $5,000 at 8% is $1.10 a day on an actual/365 basis.
What interest rate do I need to reach a goal?
Use the solve box: enter what you have, your target and the years. $10,000 to $15,000 in 8 years needs about 5.08% compounded monthly.
What is the difference between APR and APY?
APR is the yearly rate before compounding; APY includes compounding. 5% APR compounded monthly is a 5.116% APY.
Sources
- Investor.gov (SEC): Compound interest
- Consumer Financial Protection Bureau: What is the difference between APR and APY?
- TreasuryDirect: Treasury bills
Related
General information, not financial, tax or legal advice. Check important numbers with the official source before acting on them.