Simple Interest Calculator
Calculate simple interest on savings or loans. Find total interest and final balance with our easy tool.
Last updated: June 2026
Example: $5,000 at 4% Simple Interest for 3 Years
Inputs
Results
What This Means
→ This example shows how simple interest accumulates over time. Each year, you earn exactly $200 on your $5,000 principal.
→ The $200 annual interest never changes—it's always calculated on the original $5,000, regardless of how many years have passed.
→ After 3 years, you've earned $600 in total interest (3 years × $200/year), giving you a final amount of $5,600.
→ If this were compound interest instead, your final amount would be about $5,625 due to interest earning interest. The difference is small for 3 years, but the longer the timeframe, the bigger compound interest's advantage.
Our calculators are built using established financial and scientific formulas. Finance tools follow standard amortization and compound interest principles. Health tools use WHO and NIH reference standards.
Last reviewed: June 2026
Learn more about our methodology →About the Simple Interest Calculator
What Is Simple Interest?
Simple interest is straightforward: you earn the same amount of interest each year on your initial investment, with no additional interest calculated on previous earnings. While less powerful than compound interest, understanding simple interest matters for certain loans and investments, particularly short-term ones.
The formula is basic: Interest = Principal × Rate × Time
For every year you keep money invested at the same rate, you earn the same dollar amount in interest.
Simple vs. Compound Interest
Simple interest earns interest only on the principal. Each year you earn the same amount. Over 10 years at 5% simple interest, $1,000 earns $500 total.
Compound interest earns interest on both principal and previous interest. Over 10 years at 5% compound interest, $1,000 becomes $1,629 due to compounding effects.
At the same rate and time, compound interest always produces more growth than simple interest. Simple interest is rarely offered on savings accounts today (they use compound interest instead), but some loans and short-term agreements use simple interest calculations.
Real-World Applications
Short-term bonds or CDs: Some fixed-income investments use simple interest, especially shorter maturities.
Certain loan types: Some installment loans, particularly short-term loans or promissory notes between private parties, use simple interest.
Student loans: Federal student loans historically used simple interest, though they typically had subsidized portions.
How to Calculate
The formula is:
I = P × r × t
Where:
- I = Interest earned
- P = Principal (initial amount)
- r = Annual interest rate (as decimal)
- t = Time in years
Final amount = Principal + Interest
So if you invest $5,000 at 4% simple interest for 3 years:
- Interest = $5,000 × 0.04 × 3 = $600
- Final amount = $5,000 + $600 = $5,600
When Simple Interest Might Be Used
Most consumer savings accounts now use daily compound interest, which benefits savers. However, you might encounter simple interest in:
- Money market accounts — Sometimes advertised clearly
- Certain bonds or fixed-income securities
- Some personal loans between friends/family
- Certain educational savings vehicles
When evaluating investments or loans, always ask whether interest compounds or remains simple. If compound, ask how frequently it compounds.
Frequently Asked Questions
Historically, simple interest was easier to calculate before computers. Today it's mostly used for specific loan types and some short-term fixed-income products. From a borrower's perspective, simple interest is preferable (you pay less). From an investor's perspective, compound interest is preferable (you earn more).
How to Use This Calculator
- 1Enter the principal amount—the initial money you're investing or borrowing.
- 2Enter the annual interest rate as a percentage.
- 3Enter the time period in years. Simple interest can be calculated for fractions of years too.
- 4Click "Calculate Simple Interest" to see interest earned per year, total interest, and final amount.
- 5Compare this to what you'd earn with compound interest at the same rate to see the difference.