Simple interest: P×r×t
Simple interest grows linearly, no compounding. Each year adds same interest: principal × rate × time. Use for short loans and school exercises. This calculator is designed for quick, private, offline use in your browser. All formulas run locally and are verified against official sources. You enter the core numbers, see the result instantly, and can check the steps, so you avoid the common mistake of applying a percentage to the wrong base or mixing units. Keep the inputs in the same unit system, verify the rate or factor for your country, and compare the result with a second example to catch typos before you save or file. Simple interest does not compound. Each year you earn the same slice: principal times rate. Three years is just three slices stacked, not interest on interest. That is why textbooks drill A = P(1+rt)
TL;DR
- Interest = Principal × rate × years, rate as decimal.
- Formulas: I = P × r × t | A = P + I
- 5k 5% 3y — Interest 750
How it works
Interest = Principal × rate × years, rate as decimal. Total = Principal + Interest. 5k at 5% 3y → 750 interest, 5750 total. Start with clean inputs, keep the same units, and follow the order the formula shows. The tool does the arithmetic, but you decide the rate, period, or factor. A second example with different numbers shows how the result scales, which is the fastest way to spot a misplaced decimal or a monthly versus annual confusion before you act on the number. Simple interest does not compound. Each year you earn the same slice: principal times rate. Three years is just three slices stacked, not interest on
The math
r=5%=0.05. I=5000×0.05×3=750. Linear vs compound: compound would be 5788, slightly higher.
r = percent/100. t in years.
Examples
5k 5% 3y
- Interest 750
- Total 5750
10k 3.5% 7y
- Interest 2450
- Total 12450
When to use it
✦ Loans
Short-term simple loans.
✦ Teaching
Intro to interest.
⚠ Common mistakes
- Using 5 instead of 0.05
- Confusing simple with compound
FAQ (6)
When used?
Short loans, bonds, exercises.
Simple vs compound?
Simple linear, compound exponential.
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.