Find interest earned or owed using the simple (non-compounding) formula
💡 Why This Matters Not all interest works the same way — simple interest grows by a fixed amount every period, unlike compound interest which snowballs. This calculator uses the true simple-interest formula, so you get the exact number for loans, bonds, or savings scenarios that specifically use flat, non-compounding interest.
The word "simple" in simple interest isn't about ease — it's specifically about the math only touching the original principal, never the interest already earned. That's the entire distinction from compound interest.
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Simple interest is calculated with one formula: Interest = Principal × Rate × Time, where rate is the annual interest rate as a decimal and time is measured in years. Unlike compound interest, the calculation always uses the original principal — never the interest already earned — so the dollar amount of interest is identical every single period. This calculator applies that formula directly and also shows the total amount (principal plus interest) you'd end up with.
The large number is the total interest earned (or owed, if this is a loan) over the full time period. The breakdown underneath shows your original principal alongside the total amount — principal plus interest combined — which is what you'd actually receive or repay at the end of the term.
This calculator assumes true simple interest, which is less common in everyday finance than most people expect — most savings accounts, credit cards, and mortgages actually compound interest rather than applying it as a flat, non-growing rate. Before using this for a real financial product, confirm with the lender or institution whether they use simple or compound interest, since using the wrong formula can significantly under- or overestimate your actual number.
Use this to quickly check interest on financial products that explicitly state they use simple interest — some short-term loans, certain bonds, and specific savings promotions. It's also a useful teaching tool for understanding the baseline mechanics of interest before layering in the complexity of compounding.
Example: Say you invest $1,000 at 5% annual simple interest for 3 years. Interest = $1,000 × 0.05 × 3 = $150.00. Total amount after 3 years = $1,000 + $150 = $1,150.00.
Simple interest is calculated only on the original principal for the entire time period, so it grows by the same dollar amount every period. Compound interest is calculated on the principal plus any interest already earned, so it grows faster over time since you earn interest on your interest.
Multiply the principal by the annual interest rate (as a decimal) by the time in years: Interest = Principal × Rate × Time. For example, $1,000 at 5% for 3 years: 1000 × 0.05 × 3 = $150 in interest.
Simple interest shows up in some short-term loans, certain bonds, car loans in some cases, and basic savings scenarios. Most everyday financial products — savings accounts, mortgages, credit cards, most investments — actually use compound interest, so it's worth checking which one applies before assuming.