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Simple Interest Calculator

Our online tools will provide quick answers to your calculation and conversion needs. On this page, you can calculate simple interest (SI) given principal, interest rate and time duration in days, months or years. We have made it easy for you to enter daily, weekly, monthly or annually charged interest rates. e.g., 2% interest per month, 5% per week, 10% per year

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To find time period between two dates, use date duration calculator.

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Simple Interest Formula

SI = P×r×t
A = P+SI
A = P(1+rt)
A = Final amount
SI = Simple interest
P = Principal amount (Initial Investment)
r = Annual interest rate in percentage
t = Time period in years

When calculating simple interest by days, use the number of days for t and divide the interest rate by 365. Likewise, to calculate simple interest month-wise, use the number of months for t and divide the interest rate by 12.

Simple interest calculations

The following examples will show you how to solve different variables involved in simple interest calculation.

Example 1. What is the simple interest on a loan of $300 for 4 months at 12% per year?

Ans. SI = P×r×t = 300×(12/100/12)×4 = $12

Example 2. Simple interest on $5000 over 4 years is $1800, what is the interest rate?

Ans. r = SI/(P×t) = 1800/(5000×4) = 0.09 = 9%

Example 3. If you borrow $1200 at a 5% annual interest rate, how long will it take for the total amount owed to reach $1300?

Ans. SI = 1300-1200 = 100
t = SI/(P×r) = 100/(1200*(5/100)) = 1.67 years or 20 months

Example 4. Find the principal if the simple interest in 14 days at 25% per annum is 100.

Ans. P = SI/(r×t) = 100/((25/100/365)*14) = 10428.57

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