Simple Interest Calculator

Simple interest is charged or earned only on the original amount, the principal, so it grows by the same amount every year. This calculator uses I = Prt to find the interest and the total amount, shows the working, and charts the balance year by year so you can compare it with compound interest.

Try:

How to use the simple interest calculator

  1. Enter the principal (starting amount).
  2. Enter the annual interest rate and the time in years.
  3. Press Calculate to see the interest and total.

Formula

I=PrtI = Prt
A=P(1+rt)A = P(1 + rt)

Worked example: 2,000 at 4.5% for 3 years

  • Principal: 2000
  • Annual rate (%): 4.5
  • Years: 3

✓ Answer checked

I=270.00,A=2,270.00I = 270.00,\quad A = 2{,}270.00
05001000150020000: 200001: 209012: 218023: 22703principal
With simple interest the balance grows by the same amount every year, so the bars rise in a straight line.
Step-by-step working (2 steps)

  1. Simple interest formula I = Prt

    Interest is a fixed percentage of the original amount each year.

    I=Prt=2000×0.045×3=270I = Prt = 2000 \times 0.045 \times 3 = 270

  2. Total amount

    Add the interest to the principal.

    A=P+I=2270A = P + I = 2270
Formulas used
I=PrtI = Prt
A=P(1+rt)A = P(1 + rt)
How this was checked
  • ✓ Working back from the interest gives the original rate.

Frequently asked questions

What is the simple interest on 2,000 at 4.5% for 3 years?

2000 × 0.045 × 3 = 270, so the total is 2,270.

How is simple interest different from compound interest?

Simple interest is always worked out on the original amount. Compound interest also earns interest on interest already added, so it grows faster.

Can the time be in months?

Yes, as a fraction of a year: 18 months is 1.5 years.

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