Simple Interest Calculator (I = Prt)
Calculate simple interest, principal, rate, time, and total maturity amount with step-by-step formula.
Simple Interest — interactive calculator, computed instantly in your browser.
The Mechanics of Simple Interest: Linear Yields & Short-Term Loan Modeling
Simple Interest Linear Growth Curve (I = Prt)
Key Takeaway: Simple interest grows in a perfectly straight line because interest earned in prior years is not added to the principal balance for future calculations.
Simple interest is a straightforward method of calculating interest charges or investment yields based solely on the original principal amount. Unlike compound interest, accrued interest does not generate additional interest over subsequent cycles.
1. The Simple Interest Mathematical Formula
- I (Total Simple Interest): Total money earned or owed in financing fees.
- P (Principal): The initial investment or borrowed principal.
- r (Annual Interest Rate): Expressed in decimal format ($6\% = 0.06$).
- t (Time): Duration in years (or fraction of year: $\text{months}/12$, $\text{days}/365$).
- A (Maturity Amount): Total accumulated capital ($P + I$).
2. Simple vs. Compound Interest Comparison Table ($10k @ 6%)
| Duration (t) | Simple Interest ($I = Prt$) | Compound Interest ($A = P(1+r)^t$) | Difference Earned |
|---|---|---|---|
| 1 Year | $600.00 | $600.00 | $0.00 |
| 5 Years | $3,000.00 | $3,382.26 | +$382.26 |
| 10 Years | $6,000.00 | $7,908.48 | +$1,908.48 |
| 20 Years | $12,000.00 | $22,071.36 | +$10,071.36 |
🔗 Debt & Interest Cross-References
Simple interest is standard for short-term promissory notes, auto dealer add-on contracts, and basic savings bonds. For investments that re-invest accrued interest, visit our exponential 💰 Financial Hub.
Compare simple interest yields with compound growth or analyze retail discounts using the related solvers below.
Frequently Asked Questions (Simple Interest)
Simple interest is standard for short-term personal loans, automotive flat-rate financing, promissory notes, certificate of deposit (CD) non-compounding distributions, and peer-to-peer lending.
Ordinary interest (the Banker's Rule) assumes a 360-day commercial year (12 months of 30 days). Exact simple interest divides days by 365 (or 366 in leap years).
To solve for time: t = I / (P × r). To solve for rate: r = I / (P × t). To solve for initial principal: P = I / (r × t).