Simple interest calculator
Work out simple interest for any number of days, months or years, with a yearly rate or a "₹ per 100 per month" rate.
A simple interest calculator works out interest as amount × rate × time ÷ 100, on the starting amount only. ₹1,00,000 at 8% a year for 3 years earns ₹24,000 in interest.
Interest for 3 years
₹24,000.00
Rupees twenty-four thousand only
- Amount
- ₹1,00,000
- Amount + interest
- ₹1,24,000
₹666.67 a month or ₹8,000 a year in interest.
8% a year is the same as ₹0.67 per ₹100 a month.
Simple interest is charged on the starting amount only. Days are counted as a share of a 365-day year. Nothing you type is stored.
Want interest that earns interest? See the difference with the compound interest calculator.
How to use this simple interest calculator
- Enter the amount lent, borrowed or deposited.
- Choose how the rate is given. Banks quote "% a year". Informal lenders often say "₹2 per 100 a month" or "2 rupees byaj".
- Enter the rate, then choose days, months or years and enter the time.
- Read the interest, the total, and the interest for one month. Share or copy the link to keep your numbers.
Simple interest formula
SI = P × R × T ÷ 100
- SI
- Simple interest, in ₹.
- P
- The amount (principal) the interest is charged on.
- R
- The rate in % a year. For "₹ per 100 a month", R = monthly rate × 12.
- T
- Time in years. Months ÷ 12. Days ÷ 365, the common convention in India.
The total to pay back or receive is P + SI. Simple interest is always worked out on the starting amount. Interest from earlier months is never added to it, so nothing compounds.
Worked examples
₹1,00,000 at 8% a year for 3 years: 1,00,000 × 8 × 3 ÷ 100 = ₹24,000. The total is ₹1,24,000.
₹50,000 at 7% a year for 200 days: T = 200 ÷ 365, so the interest is 50,000 × 7 × 200 ÷ 365 ÷ 100 = ₹1,917.81.
- Amount
- ₹50,000
- Interest (200 days)
- ₹1,917.81
- Amount + interest
- ₹51,917.81
"₹ per 100 per month" rates in % a year
In informal lending, interest is often quoted as rupees per ₹100 per month. Multiply by 12 to get the yearly rate. Here is what each rate means on ₹1 lakh:
| ₹ per 100 a month | % a year | Interest a month on ₹1 lakh | Interest a year on ₹1 lakh |
|---|---|---|---|
| ₹0.50 | 6% | ₹500 | ₹6,000 |
| ₹1 | 12% | ₹1,000 | ₹12,000 |
| ₹1.50 | 18% | ₹1,500 | ₹18,000 |
| ₹2 | 24% | ₹2,000 | ₹24,000 |
| ₹3 | 36% | ₹3,000 | ₹36,000 |
A rate that sounds small each month can be large over a year. "₹3 per 100" is 36% a year.
Simple interest vs compound interest
With compound interest, each year's interest is added to the amount and earns interest too. Take ₹1,00,000 at 10% a year for 3 years:
- Simple interest
- ₹30,000
- Compound interest (yearly)
- ₹33,100
The gap grows with time and rate. Most bank deposits compound, so use the compound interest calculator or the FD calculator for them.
Simple interest calculator FAQs
What is the simple interest formula?
SI = P × R × T ÷ 100. P is the amount, R the rate in % a year and T the time in years. For months, use months ÷ 12; for days, days ÷ 365.
What is the interest on ₹1 lakh at 12%?
₹12,000 for one year, which is ₹1,000 a month. For 3 years it is ₹36,000.
How do I turn a monthly rate into a yearly rate?
Multiply by 12. ₹2 per ₹100 a month is 2 × 12 = 24% a year. To go the other way, divide the yearly rate by 12.
What is the difference between simple and compound interest?
Simple interest is charged on the starting amount only. Compound interest is also charged on earlier interest, so it grows faster. ₹1 lakh at 10% for 3 years gives ₹30,000 simple interest and ₹33,100 compound interest.
Why divide days by 365?
It is the common convention in India for interest by the day. Some lenders use other day counts, so check your agreement if the figure must match to the rupee.
Is my data saved?
No. Everything is calculated in your browser. Nothing you type is sent to us or stored. The only place your numbers go is the link you choose to copy or share.
For education only. This is not investment or legal advice, and we are not SEBI-registered advisers. Check the actual terms of any loan or deposit before you rely on these figures.