Simple interest calculator: interest and total
Simple interest math is principal×rate×time: 10,000 at 5% for 3 years earns 1,500 interest for 11,500 total. No compounding here: every year earns on the original principal only. This calculator is built for fast, private, offline use in your browser. Every formula runs locally and is verified against official sources. You enter the key numbers, see the result instantly and check the steps.
TL;DR
- Zero rate gives zero interest at any horizon.
- Formulas: I = P×r×t | total = P + I
- Example 1: 10,000 at 5% for 3 years — Interest: 10,000×0.05×3 = 1,500
How it works
Interest = principal×rate×years; total = principal + interest. Zero rate gives zero interest at any horizon. Start with clean data, keep the same units and follow the order in the formula. The tool does the arithmetic, you choose rate, period or factor. A second example with different numbers shows how the result scales.
The math
10,000×0.05×3=1,500 interest, total 10,000+1,500=11,500. Zero check: 5,000×0×10=0 interest, total 5,000.
Linear growth on principal only. Rate as decimal: 5% = 0.05.
Examples
Example 1: 10,000 at 5% for 3 years
- Interest: 10,000×0.05×3 = 1,500
- Total: 10,000+1,500 = 11,500
- Each year earns the same 500
Example 2: 5,000 at 0% for 10 years
- Interest: 5,000×0×10 = 0
- Total: 5,000
- Zero rate never grows
When to use it
✦ Short loan cost
Price a 3-year loan: interest and total repayment from principal and rate.
✦ Late payment
Statutory simple interest on 5,000 owed: total after the delay.
⚠ Common mistakes
- Percent as decimal: 5% is 0.05, not 5, a hundredfold error.
- Compounding it: simple interest never earns on interest, use compound for that.
- Years vs months: convert months ÷12 first, rate is yearly.
FAQ (6)
10,000 at 5% for 3 years?
1,500 interest, 11,500 total.
Yearly slice?
500 per year, same every year.
If I type my salary or prices here, do you store them?
No — and that's deliberate. Everything runs locally in your browser, nothing leaves your device. We don't see your net salary, your margins, or the VAT numbers you test. For a finance tool that matters: you can run a quick check on a payslip or an invoice while on public Wi-Fi and close the tab knowing no trace is kept server-side.
Can I use it on the train without signal to check an invoice?
Yes. Load the page once, then it works offline. VAT, discount and mortgage math are all pure JavaScript — no API call. I often test it in airplane mode: open the mortgage page, type 250,000 at 4.5% for 25 years, you get the schedule instantly, even in a tunnel.
Can I file taxes with these results?
Use it as a fast sanity check, not as the final filing. Formulas are standard (e.g. Net = Gross / 1+VAT) and verified against official sources listed at the bottom, but rates and thresholds change — Italy's 22% vs Germany's 19%, or IRPEF brackets. For the actual declaration, double-check with your accountant or Agenzia delle Entrate / HMRC / IRS.
How do I send a calculation to my accountant?
Hit 'Share Link' under the results. It encodes the inputs in the URL — e.g. ?price=1200&vat=22 — so your accountant opens the exact same view, no screenshot needed. You can also copy the result with one tap and paste it into an email.
Sources & References
⚠ Financial Disclaimer
This tool provides estimates for informational purposes only and does not constitute financial, tax, or legal advice. Results may vary based on local regulations, rates, and individual circumstances. Always consult a qualified professional before making financial decisions.
How this calculator is maintained
This calculator is written and maintained by Davide Coronese, independent developer and founder of CalcTracker.
Methodology: every formula is checked against official publications and validated by an automated test suite before release. Health, tax and finance pages cite the exact sources they rely on.
Found an error? Contact us — verified corrections ship within 24 hours.