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Simple Interest Calculator

Work out simple interest from the principal, the yearly rate and the time, or turn the formula around and find whichever of the four values is missing. Time can be typed in years, months or days. The page shows the formula with your numbers substituted, so it also works as a homework checker.

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Calculate Simple Interest

Simple interest is charged only on the original principal: I = P × R × T ÷ 100, with T in years. Months count as 1/12 of a year and days as 1/365. Money is rounded to 2 decimals (half up) only for display.

The amount lent or invested.

How to Use the Simple Interest Calculator

  1. Choose what to find: interest, principal, rate or time.
  2. Fill in the other boxes (the box you are solving for is hidden) and pick the time unit.
  3. Press Calculate.
  4. Read the answer and the formula with your numbers.

About This Tool

Students practising the I = PRT/100 formula, people checking a simple-interest loan or deposit quote, and small lenders working out interest on short-term amounts.

Input: Numbers  ·  Output: Interest.

Features and Limitations

Features

  • Solves for interest, principal, rate or time.
  • Time in years, months or days.
  • Total amount and yearly interest shown.
  • Exact fractions: no floating-point rounding errors.
  • Formula with the numbers filled in.

Limitations

  • Simple interest only; interest is not added back to the principal. Use the compound interest calculator for that.
  • Days use a 365-day year; banks using actual/360 or leap-year rules give slightly different amounts.
  • The rate is per year, and fees or taxes are not included.
  • Results are computed in your browser; nothing you enter is sent to a server.

Example

₹50,000 at 6.5% for 3 years: interest = 50,000 × 6.5 × 3 ÷ 100 = ₹9,750 and the total amount is ₹59,750. Solving back, the time needed to earn ₹9,750 on ₹50,000 at 6.5% is 3 years.

Frequently Asked Questions

What is the simple interest formula?

I = P × R × T ÷ 100, where P is the principal, R the yearly rate in percent and T the time in years. The total amount is A = P + I.

How do I find the principal, rate or time?

Rearrange the formula: P = I × 100 ÷ (R × T), R = I × 100 ÷ (P × T), and T = I × 100 ÷ (P × R). The calculator does this when you choose the quantity to find.

How do I use months or days?

Convert to years first: months ÷ 12, days ÷ 365. For example 9 months is 0.75 years, and 90 days is 90 ÷ 365 = 0.2466 years.

What is the difference between simple and compound interest?

Simple interest is paid on the original principal only, so it grows by the same amount every year. Compound interest is paid on the principal plus earlier interest, so it grows faster over time.

Why is the time sometimes shown as a decimal?

When solving for time the answer is in years and is rarely a whole number, so the page also gives it in months and days so you can read it easily.

Related Tools

More like this: all Finance tools, all Calculators tools or the TinySandy home page.