Simple Interest Calculator
Interest and total amount — or the missing principal, rate or time — with the formula.
How this was calculated
Results are estimates for general information and planning, not financial advice. Banks and institutions may calculate differently (rounding, fees, rate changes). Confirm figures with your lender or a qualified adviser before deciding.
About the Simple Interest Calculator
Simple interest is earned or charged only on the original amount — the principal — never on interest already added. It is used for many short-term loans and deposits, for interest between two dates, and in school and exam maths.
Enter the principal, the annual rate and the time — in years, months or days, or as two dates — to get the interest and the total amount. Or solve for whatever is missing: the principal, the rate or the time, from the interest or from the total amount. For days and dates you can choose the day-count convention; Actual/365 is the default.
How to use it
- Choose what to calculate: interest, principal, rate or time.
- Enter the values you know. When solving for the principal, rate or time, say whether you know the interest or the total amount.
- Enter the time as a duration in years, months or days, or switch to Between dates. For days and dates, choose the day count (Actual/365 if unsure).
- Read the result, the total amount and the interest per month. The formula panel shows every step.
Examples
Interest ₹12,000 · total amount ₹62,000
Actual/365: ₹197.26 · Actual/360: ₹200.00
212 days · interest ₹4,065.75 (Actual/365)
8% a year
1 year 3 months (1.25 years)
The simple interest formula
SI = P × R × T ÷ 100 and A = P + SI
- P is the principal, R the rate in percent per year and T the time in years
- Months are divided by 12; days are divided by the day-count basis (365 by default)
Rearranged: P = 100 × SI ÷ (R × T), R = 100 × SI ÷ (P × T) and T = 100 × SI ÷ (P × R). From a total amount A, the principal is P = A ÷ (1 + R × T ÷ 100).
Day-count conventions
When the time is in days, the result depends on how a year is counted:
- Actual/365 (Fixed): actual days ÷ 365, even in a leap year. The default here.
- Actual/360: actual days ÷ 360, so a full year of interest builds up in 360 days. Common for money-market loans in many countries.
- Actual/Actual (ISDA): the days in each calendar year ÷ that year's length (365 or 366). Needs dates.
- 30E/360 (Eurobond basis): every month counts as 30 days and day 31 becomes 30. Needs dates.
Between two dates the end date is not counted: 1 January to 2 January is one day. Your loan or deposit agreement says which convention applies.
Limitations
- Simple interest only: if interest is added to the balance during the term, use the compound interest calculator instead.
- Tax deducted on interest, fees and penalties are not included.
- When solving for the time, days are shown on a 365-day year.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
What is the formula for simple interest?
SI = P × R × T ÷ 100, where P is the principal, R the annual rate in percent and T the time in years. For ₹50,000 at 8% for 3 years: 50,000 × 8 × 3 ÷ 100 = ₹12,000.
How do I calculate simple interest for days?
Convert the days into years with the day-count basis: T = days ÷ 365 under Actual/365. ₹10,000 at 8% for 90 days earns 10,000 × 8 × (90 ÷ 365) ÷ 100 = ₹197.26.
Why do Actual/365 and Actual/360 give different interest?
Actual/360 divides by a shorter year, so the same number of days is a larger fraction of a year and earns about 1.4% more interest (365 ÷ 360). Lenders state which convention a loan uses.
Is simple interest better than compound interest?
For a borrower, simple interest costs less because interest is never charged on interest. For a saver, compound interest earns more over the same time. Below the result, the calculator shows what yearly compounding would give for comparison: interest is added to the balance after each full year, and any part-year earns simple interest, so for a year or less the two are the same.