Decision tools built for clarity
Simple Interest Calculator
Calculate non-compounding simple interest for years, months, or an explicit day-count basis.
Enter the required values, select the applicable options, and calculate.
This educational estimate excludes fees, compounding, variable rates, and lender-specific conventions.
Methodology
Formula or transformation
Applies interest equals principal times annual rate times time without compounding.
Variables
- Starting principal
- Annual rate
- Time expressed in years
- Simple interest
Units
- Currency
- Percent
- Year
- Day
Rounding policy
Canonical arithmetic retains declared precision before currency display rounding.
Interest equals principal multiplied by the annual rate and time in years; day durations require a visible 365- or 360-day basis.
Calculate non-compounding simple interest for years, months, or an explicit day-count basis.
Reviewed sources
- CFPB — Calculating loan payments worksheet Reviewed on 2026-09-07
Formula review history
-
Initial formula, day-basis, and source review.
Reviewed 2026-09-07 for formula version simple-interest-prt-v1
Assumptions
- Inputs are interpreted using the displayed units and options.
- The calculation follows the methodology and factors listed in the sources.
Limitations
- Display rounding can hide additional decimal places.
- The calculation cannot add accuracy that is absent from the submitted inputs.
- This educational estimate excludes fees, compounding, variable rates, and lender-specific conventions.
Worked example
A principal of 1,000 at 5% for two years produces interest of 100 and a total of 1,100.
Frequently asked questions
Are the calculations deterministic?
Yes. The same valid inputs and options produce the same canonical result.
Can I use decimal values?
Use decimal values where the displayed input accepts them.