# Simple Interest Calculator I = Prt

## Calculator Use

Calculate simple interest on the principal only, I = Prt. Simple interest does not include the effect of compounding.

## Simple Interest Formula

I = Prt

Where:

- P = Principal Amount
- I = Interest Amount
- r = Rate of Interest per year in decimal; r = R/100
- R = Rate of Interest per year as a percent; R = r * 100
- t = Time Periods involved

Notes: Base formula, written as I = Prt or I = P × r × t where rate r and time t should be in the same time units such as months or years.

Time conversions that are based on day count of 365 days/year have 30.4167 days/month and 91.2501 days/quarter. 360 days/year have 30 days/month and 90 days/quarter.

## Simple Interest Formulas and Calculations:

This calculator for simple interest-only finds I, the simple interest where P is the Principal amount of money to be invested at an Interest Rate R% per period for t Number of Time Periods. Where r is in decimal form; r=R/100. r and t are in the same units of time.

- Calculate Interest, solve for I
- I = Prt

- Calculate Principal Amount, solve for P
- P = I / rt

- Calculate rate of interest in decimal, solve for r
- r = I / Pt

- Calculate rate of interest in percent
- R = r * 100

- Calculate time, solve for t
- t = I / Pr