How to use
- Choose what you want to find: interest, principal, rate or time.
- Enter the other values. For the time, pick years, months or days.
- Read the result, the interest, the total amount and the calculation below it.
Formula
Simple interest SI = P × R × T ÷ 100, where P = principal, R = yearly rate (%) and T = time in years. Total amount = P + SI. Months are divided by 12 and days by 365 to get years. Example: ₹1,00,000 at 8% for 3 years gives 1,00,000 × 8 × 3 ÷ 100 = ₹24,000.
Tips and common uses
Quick check by hand
Interest per year is the principal × rate ÷ 100. For ₹1,00,000 at 8% that is ₹8,000 a year, so 3 years is ₹24,000. Simple interest adds the same amount every year.
Money lent to friends and family
For a personal loan, write down the amount, the rate, the start date and the repayment date, and get both people to sign. Choose months or days here if you repay part-way through a year.
Check the rate period
The rate must be per year. If someone quotes 2% a month, the yearly rate is 24%, so enter 24.
Frequently asked questions
What is the simple interest formula?
SI = P × R × T ÷ 100. P is the principal, R is the interest rate per year in percent and T is the time in years. For example, ₹50,000 at 10% for 2 years gives 50,000 × 10 × 2 ÷ 100 = ₹10,000.
How do I calculate simple interest for months or days?
Change the time into years first: divide months by 12 and days by 365. Six months is 0.5 year, so ₹1,00,000 at 12% for 6 months earns 1,00,000 × 12 × 0.5 ÷ 100 = ₹6,000. This calculator does it for you when you choose months or days.
What is the difference between simple and compound interest?
Simple interest is worked out only on the original principal, so it grows by the same amount every year. Compound interest is also charged on the interest already added, so it grows faster. Use our Compound Interest Calculator to compare.
How can I find the rate or the time?
Rearrange the formula: R = SI × 100 ÷ (P × T) and T = SI × 100 ÷ (P × R). Choose "Interest rate" or "Time period" above and enter the other values.
Is the result what my bank or lender will charge?
Only if they use simple interest. Most bank loans, deposits and credit cards use compound interest or reducing-balance interest, so their figures will differ. Use this for personal loans between people and for school and exam problems.