Simple Interest Calculator — Free Online Tool
Calculate interest on loans or deposits with the SI formula. · No signup · Works on mobile
100% private: your data is processed in your browser. Nothing is uploaded to our servers.
How to use the simple interest calculator
-
1
Enter the principal amount borrowed or invested.
-
2
Set the annual interest rate and the duration in years, months, or days.
-
3
Read the interest and the total amount (principal + interest) instantly.
What does this tool do?
This free simple interest calculator computes interest earned or owed using the classic SI = P × R × T ÷ 100 formula. Enter the principal, annual rate, and time period to instantly see the interest amount and the total maturity value — ideal for quick loan checks and school problems.
How does the simple interest calculator work?
Simple interest is charged only on the original principal, never on accumulated interest. The tool multiplies principal × annual rate × time in years, and also accepts months or days (converted as t/12 or t/365).
Frequently Asked Questions
Where is simple interest actually used?
Simple interest applies to most car loans, short-term personal loans, bonds' coupon payments, and late-payment penalties. For example, ₹50,000 at 8% simple interest for 3 years earns exactly ₹12,000 — the interest is identical every year because it never compounds.
How do I calculate simple interest for months instead of years?
Convert months to years by dividing by 12. For ₹20,000 at 12% annual rate for 9 months: SI = 20000 × 12 × (9/12) ÷ 100 = ₹1,800. This calculator has a months option that handles the conversion automatically.
Is the simple interest calculator really free?
Yes — 100% free with no hidden charges, trial limits, or premium tiers for core features. You don't need to create an account or enter an email address. The site is supported by non-intrusive display ads, which keeps every tool free for everyone.
Is my data private when using the simple interest calculator?
Completely. The simple interest calculator runs entirely in your browser using JavaScript — nothing you type or upload is sent to our servers. When you close the tab, your data is gone. This makes it safe for confidential documents, financial figures, and personal information.
Does the simple interest calculator work on mobile phones?
Yes. The simple interest calculator is built mobile-first and works on any phone or tablet with a modern browser — iPhone (Safari), Android (Chrome), and everything in between. The layout adapts to small screens, so buttons and inputs stay easy to tap on a 375px-wide display.
Do I need to install anything to use the simple interest calculator?
No. The simple interest calculator works directly in your web browser — no downloads, no extensions, no signup. Just open the page, use the tool, and get your result instantly. It works on Windows, macOS, Linux, ChromeOS, iOS, and Android.