Simple interest program in Python

Simple interest = principal × rate × time / 100, where the rate is a percentage per year.

The program

principal = float(input("Principal: "))
rate = float(input("Rate per year (%): "))
years = float(input("Time (years): "))

interest = principal * rate * years / 100
total = principal + interest

print(f"Simple interest = {interest:.2f}")
print(f"Total amount    = {total:.2f}")

Typed in this example: 10000, 7.5, 3. Press Run to type your own.

Principal: 10000
Rate per year (%): 7.5
Time (years): 3
Simple interest = 2250.00
Total amount    = 12250.00

How it works

• Each input() asks one question, and float() turns each answer into a number.
• The interest is 10000 × 7.5 × 3 / 100 = 2250.
• :.2f prints money with exactly two decimal places.

Banks usually use compound interest, where the interest is added to the principal every period: principal * (1 + rate / 100) ** years. For the same numbers that gives 12422.97.

Related programs: Compound interest.