Source-linked deep guide
Simple Interest Calculator: interest on the starting amount
Simple interest grows from the original principal only. The simple interest calculator does not add interest to past interest.
Think of earning the same sticker reward each week. Your new stickers do not create extra stickers later.
Core Formula
I = P × r × t
This finds the interest amount. Add the interest to the principal to estimate the total.
Total amount formula
A = P + I
The total amount is the starting principal plus the interest earned or charged.
Step-by-step example
Find simple interest on $500 at 6% for 3 years.
- Change 6% to a decimal: 6 ÷ 100 = 0.06.
- Use the formula: I = P × r × t.
- Substitute the numbers: I = 500 × 0.06 × 3.
- Calculate: I = 90.
- Add principal: 500 + 90 = 590.
- The interest is $90, and the total is $590.
Simple interest vs compound interest
Common mistakes and edge cases
- Do not use 6 as the decimal for 6%. Use 0.06.
- Zero time gives zero interest. No time passed, so no interest accumulates.
- Negative rates need context. They may represent a loss, fee, or special financial model.
- Real loans may include fees. Simple interest alone may not show the full cost.
Sources and accuracy notes
Simple interest is commonly defined as interest calculated on the principal only, while compound interest also uses accumulated interest. See Investopedia: Simple vs. compound interest.
CalculTools rounds currency outputs to cents. This page is educational and does not replace lender terms or financial advice.
FAQ
What should I check before using this money result?
Confirm the rate, term, fees, compounding assumptions, taxes, and whether the result is before or after deductions.
Is this financial advice?
No. This calculator provides an educational estimate. Use official lender, tax, payroll, or professional guidance for decisions.
What should I check before using this result?
Check the input units, the formula shown on the page, and any assumption that does not match your situation.
What if the result looks off?
Recheck the values and units first. If the formula or label looks wrong, send the page URL and example values through the contact page.