Simple Interest Calculator

Calculate interest on your principal in seconds — enter your amount, rate, and time to see your returns or loan cost in Naira.

Loan / Savings Details

Principal Amount

₦

Annual Interest Rate

Time Period (Years)

yrs

Simple Interest

₦150,000

Principal

₦500,000

Interest Earned

₦150,000

Total Amount

₦650,000

Effective Return

30.0%

How to Use This Calculator

Calculate Tab

Enter your principal amount (the starting sum), the annual interest rate, and the time period in years. The calculator instantly shows your total simple interest and the final amount you will receive or owe.

Compare Rates Tab

Enter the same principal and compare two different rate/time combinations side by side. Useful for deciding between a short-term high-rate deal and a longer-term lower-rate offer.

The Formula

SI = P × R × T ÷ 100 Where: SI = Simple Interest (₦) P = Principal amount (₦) R = Annual interest rate (%) T = Time period (years) Total Amount = P + SI

Simple interest is calculated only on the original principal — unlike compound interest, previously earned interest does not itself earn interest. This makes it straightforward to calculate and easy to compare across products.

Example

Scenario: Short-term Loan

Emeka borrows ₦500,000 from a cooperative society at 15% per annum simple interest for 2 years.

Principal (P)₦500,000

Rate (R)15% per annum

Time (T)2 years

SI = 500,000 × 15 × 2 ÷ 100₦150,000

Total repayment₦650,000

Emeka owes ₦150,000 in interest. At a bank offering 22.5% simple interest for the same period, the interest would be ₦225,000 — ₦75,000 more costly. Always compare rates before committing.

FAQ

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus previously accumulated interest. Over long periods compound interest grows much faster, which is why savings accounts and investments use it while short-term loans often use simple interest.

Most Nigerian commercial banks use compound interest for savings and deposit accounts. However, some cooperative loans, microfinance products, and informal lending arrangements quote simple interest. Treasury Bills effectively use simple interest since they are discount instruments with no interim compounding.

Rates vary widely. Commercial bank lending rates typically range from 20–35% per annum. Microfinance banks may charge 2–5% per month (24–60% per annum). Cooperative societies usually offer 5–15% per annum. Always ask for the annual percentage rate (APR) to compare accurately.

For simple interest, multiply the monthly rate by 12. A 2% monthly rate equals 24% per annum (simple). Enter that annual rate into this calculator to see your total interest over any period.

Simple interest is generally better for borrowers because interest does not compound on top of itself. For lenders and savers, compound interest is preferable because it generates higher returns over time. When borrowing, look for simple interest products; when saving or investing, look for compound interest.