Calculate simple interest — the interest and total on a principal at a flat annual rate over time, with no compounding.
Simple interest does not compound — it's charged only on the original principal. Many real loans and savings use compound interest instead. General information only.
Simple interest is charged only on the original principal, so it grows in a straight line. Compound interest is charged on the balance including prior interest, so it accelerates. Short-term loans and some bonds use simple interest; most savings and credit use compound.
Interest = Principal × rate × time
Simple interest appears on some short-term and auto loans and certain bonds. Savings accounts, credit cards, and mortgages generally compound.
Add the simple interest to the principal. This calculator shows both.
Related: compound interest calculator · loan calculator · CD calculator · all free calculators.
More free saving, debt & loans tools — no signup, works on any device.
Yes. The Simple Interest Calculator is completely free, runs in your browser, and never asks for a signup, email, or download. Enter your numbers and the result updates instantly.
It uses standard formulas and recalculates the moment you change a value, so the math is exact for the inputs you enter. Treat the result as a reliable planning estimate; for decisions with legal or tax consequences, confirm the figures with a qualified professional.
Yes. The calculator is mobile-friendly and works on any phone, tablet, or computer — there is no app to install and nothing to save.
Yes. Scroll to “Add this free calculator to your site” above and copy the embed snippet to place the live calculator on your blog or website for free.
Last reviewed: September 2026. Free to use, no signup — Simple Interest Calculator by ToolWise Digital.
Copy the snippet to embed the live calculator on your blog or website — free for any site. The small “Calculator by ToolWise Digital” credit line keeps it free; you're welcome to remove it, but we appreciate you leaving it.
Ready-made Google Sheets & Excel trackers for money, taxes, and small business — each with a free phone version.
Browse the shop →Subscribe and we'll email you our Simple Monthly Budget (Google Sheets & Excel, plus a phone version) — free. Then the occasional short note on pricing, bookkeeping, and the money side of a small business. No spam — unsubscribe anytime.