Simple Interest Calculator
Calculate simple interest and total amount.
How to use this tool
- Enter principal, annual rate and years in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your interest and the full breakdown beneath it.
Calculate simple interest and total amount.
⚠ This tool provides general estimates for education only and is not financial, tax or legal advice. Figures may not reflect your situation — verify with a qualified professional.
Formula
Interest = Principal × Rate × Time ÷ 100
Total = Principal + Interest
I = P × r × t where r is expressed as a decimal (rate ÷ 100)
How it works
This calculator applies the simple interest formula, which assumes that interest is earned only on the original principal — not on previously accumulated interest. The interest amount is computed as the product of the principal, the annual rate (converted from a percentage), and the number of years. This method is commonly used for short-term loans, certificates of deposit, and basic savings estimates.
Note that simple interest does not account for compounding; for investments or loans that compound periodically, the actual interest earned or owed will differ from this result.
Worked example
- Principal = $1,000; Annual rate = 5%; Years = 2
- Interest = 1,000 × 5 × 2 ÷ 100 = 1,000 × 0.05 × 2 = $100
- Total = Principal + Interest = $1,000 + $100 = $1,100
Interest = $100; Total = $1,100
Common mistakes to avoid
- Using years as a decimal for months (e.g., entering 0.5 for 6 months) without confirming the time unit the calculator expects — a mismatch inflates or deflates the result.
- Applying simple interest to a savings account that compounds, understating actual interest earned.
- Forgetting to express the rate as a percentage — entering 0.05 instead of 5 gives interest 100x too small.
Key terms
- Principal
- The initial sum of money deposited or borrowed, before any interest is applied.
- Simple interest
- Interest calculated solely on the original principal, not on accumulated interest from prior periods.
- Annual rate
- The yearly percentage rate used to compute interest for one year.
- Maturity value
- The total amount (principal plus interest) owed or received at the end of the term; called 'Total' in this calculator.
Frequently asked questions
- When is simple interest actually used?
- Simple interest applies to many short-term loans, some car loans (common in the US), some bonds, and treasury bills. Most savings accounts use compound interest instead.
- What is the difference between simple and compound interest?
- Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus previously earned interest, so the balance grows faster over time.
- How much interest does $1,000 earn at 5% for 3 years (simple)?
- $1,000 x 0.05 x 3 = $150 in simple interest; total = $1,150. With annual compounding the total would be $1,157.63.