Savings calculator
Simple Interest Calculator
Estimate interest when interest is calculated only on the original principal, not on accumulated interest.
Updated: June 10, 2026
Calculate simple interest
Formula
Simple interest equals principal × annual rate × time. Final amount equals principal plus simple interest.
Worked example
$5,000 at 4% simple interest for 3 years earns $600 before any fees, taxes, or other adjustments.
When simple interest is useful
Simple interest is useful when you want to isolate the rate, principal, and time without the extra effect of compounding. It can be a helpful classroom example and may also describe some short-term interest calculations where interest does not earn additional interest.
If a product advertises APY, monthly compounding, daily compounding, or reinvested interest, a compound-interest calculation is usually a better match.
Common mistakes
Make sure the time field uses years, not months. Six months should be entered as 0.5 years. Also remember that taxes, account fees, promotional rules, and minimum balances are not included in the estimate.
How to read the result
Interest earned is the dollar amount generated by the principal over the selected time. Final amount adds that interest to the starting principal. Effective growth shows the total interest as a percentage of the starting principal, not an annualized APY.
Assumptions and limits
- The rate is treated as a fixed annual simple-interest rate for the full period.
- No deposits, withdrawals, compounding, fees, penalties, or taxes are included.
- The estimate assumes interest is calculated on the original principal only.
Next steps
Use this result as a baseline for non-compounding math, then compare it with compound growth or APY scenarios if interest is reinvested. For a savings target, try the savings goal calculator.
FAQ
Does this compound monthly?
No. It is intentionally a non-compounding calculation.
When is simple interest used?
Some loans, short-term notes, and educational examples use simple-interest math.
Can fees change the result?
Yes. Fees, taxes, and contract-specific rules are not included in this simplified estimate, so real-world outcomes can differ.
How to read this non-compounding baseline
Read interest earned, final amount, and effective growth together. This page is most useful when it isolates straight-line rate math before you compare it with compounding products, fee drag, or reinvestment assumptions.
Before acting, compare result with note terms, account disclosures, lender or issuer documents, and any tax treatment that changes net return. See How We Calculate and the Disclaimer for more context.
Method and verification trail
- Method used: Simple interest is calculated from principal × annual rate × time, then added back to original principal without compounding.
- Primary source type to verify: Loan note, savings disclosure, classroom formula reference, or contract terms that explicitly use non-compounding interest.
- What to confirm in real documents: Whether quoted rate is truly simple interest, whether time should be measured in years or day-count convention, and whether fees, taxes, or accrued-interest timing change practical outcome.
- Scope limit: This page does not model reinvestment, compounding, irregular cash flows, changing rates, or institution-specific posting rules.
For site-wide methodology, review How We Calculate. For sourcing and corrections standards, review Editorial Policy.