Simple Interest Calculator
Adjust the inputs below. Results update as you type.
How it works
Simple interest: I = P × r × t. Total = P + I. Unlike compound interest, principal doesn't grow—interest accrues only on the original amount. Used for short-term loans, savings bonds, and some car loans. For t in days: use t = days/365 (actual/actual) or days/360 (bank basis). Compound interest always outperforms simple interest for the same rate over the same period.
Input guidance
- Use realistic rates from lender or provider quotes instead of headline averages.
- Model conservative, baseline, and optimistic scenarios before deciding.
- Include recurring real-world costs (fees, taxes, insurance, maintenance) where relevant.
The formula
Simple interest is I = P · r · t, charged only on the original principal. The final amount is A = P · (1 + r · t).
Worked example
$2,000 at 5% simple interest for 4 years earns 2000 × 0.05 × 4 = $400, for a $2,400 total — no compounding involved.
More examples to test
- Conservative case: use a higher interest rate and lower growth assumptions to stress-test affordability.
- Optimistic case: use a lower rate with stable income assumptions to compare upside potential.
How to interpret results
Treat this as a planning model, not a final approval tool. Compare at least two scenarios and focus on total-cost and cash-flow trade-offs.
When this can be inaccurate
Results can diverge due to fees, changing rates, tax rules, lender policies, and behavior changes that simplified models cannot fully capture.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
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Frequently asked questions
When is simple interest used?+
Short-term loans, some car loans, and certain bonds. It is easy to compute because interest never compounds on itself.
How does it differ from compound interest?+
Simple interest ignores past interest; compound interest adds it to the balance, so compound grows faster over the same period and rate.
Does the time unit matter?+
Yes — rate and time must use the same unit. An annual rate pairs with years; a monthly rate pairs with months.
How should I use this result?+
Treat it as a planning estimate. Compare at least two realistic scenarios, then confirm with statements, quotes, or a qualified professional before acting.
How often should I refresh assumptions?+
Refresh whenever rates, income, costs, or policy limits change materially, and before making irreversible commitments.