Simple Interest Calculator
Calculate simple interest with the classic P × R × T formula.
Simple interest
1,800.00
Total amount: 11,800.00
Principal
10,000.00
Total amount
11,800.00
Time in years
3.0000
Compound equivalent
1,910.16
Annual compounding
I = P × R × T ÷ 100 = 10,000.00 × 6 × 3.0000 ÷ 100
- Compounding annually instead would earn 110.16 more over the same period.
- Amounts are shown as plain numbers so the result works in any currency.
What does Simple Interest Calculator do?
Work out simple interest on a principal over any period, and see the total amount payable. Simple interest is charged on the original principal only, which makes it far cheaper than compound interest over long terms.
How to Use Simple Interest Calculator
- 1Enter the principalThe amount borrowed or invested.
- 2Enter the annual rateThe yearly interest percentage.
- 3Enter the timeIn years, months or days.
Key Features
- Interest and maturity amount from principal, rate and time
- Time entered in years, months or days
- Side-by-side comparison with compound interest on the same inputs
- Solve for any variable: find the rate or time needed for a target interest
Frequently Asked Questions
What is the simple interest formula?
I = P × R × T ÷ 100, where P is principal, R is the annual rate as a percentage and T is time in years. The total amount is P + I.
How is simple interest different from compound interest?
Simple interest is always calculated on the original principal. Compound interest is calculated on the principal plus interest already earned, so it accelerates. Over 10 years at 8%, £10,000 earns £8,000 simple but £11,589 compound.
Where is simple interest actually used?
Short-term personal loans, car loans in some markets, treasury bills, and most exam questions. Long-term savings and mortgages nearly always compound.
How do I calculate interest for a number of days?
Switch the time unit to days. The calculator divides by 365, which is the common convention; some lenders use 360, so check your agreement if the amount matters.
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