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Simple Interest Calculator

Calculate interest without compounding, with clear year, month and day-count assumptions.

Your numbers

Make it your own
Updates as you type
Simple interest
$100.00

USD · rounded to the nearest cent

Final amount$1,100.00
Time in years2

No compounding. Day input uses the explicitly selected 360- or 365-day basis; actual/actual calendar accrual is not modeled.

Your calculation, step by step

No black boxes
  1. I = P × r × t = 1000 × 0.05 × 2.

What if things were different?

Save up to three scenarios, then change your inputs to compare the possibilities.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

I = P × r × t

Simple interest is earned on principal only. Months are divided by 12. Day-based calculations use the selected fixed 360- or 365-day denominator, rather than a calendar actual/actual convention. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.

A worked example

Interest on $1,000 for 2 years at 5% is 1,000 × 0.05 × 2 = $100. Final amount is $1,100.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

What assumptions does this calculation use?

Simple interest is earned on principal only. Months are divided by 12. Day-based calculations use the selected fixed 360- or 365-day denominator, rather than a calendar actual/actual convention.

Can I save or check a scenario?

The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.

Sources & methodology

This calculator uses the mathematical identity and assumptions stated above. No current rates, prices, or external data are loaded. Conversion tools use international unit definitions.

Formula review: October 24, 2026. Read our methodology.