Free online tool
Simple Interest Calculator
The classic P × R × T formula, calculated instantly.
Simple vs compound interest
Simple interest is calculated only on the original principal — interest earned doesn't itself earn more interest. That's the opposite of compounding, where each period's interest is added to the balance for the next period. Because of this, simple interest is easier to compute but produces smaller totals over long periods.
Where you'll see it
Simple interest is most common in short-term personal loans, car loans, some bonds, and quick lending arrangements between individuals. Most modern savings products and mortgages, on the other hand, use compound interest — which usually favours the lender or the saver, depending on which side you're on.
+How is monthly interest calculated?
Divide the annual rate by 12. For a 6% annual rate, monthly interest on $1,000 is $5.
+When is simple interest better for me?
As a borrower, simple interest is almost always cheaper than compound — you'll pay interest only on the original principal, not on prior interest.
The straight-line cousin of compound growth
Simple interest only ever applies to the original principal, calculated as principal multiplied by rate multiplied by time. There's no reinvestment of earned interest, so the growth is linear rather than curved, which makes it easier to predict but generally slower to build wealth than compounding over long periods.
Because the calculation never changes from period to period, simple interest is popular anywhere clarity matters more than maximising returns — short-term consumer loans, certain promissory notes, and some fixed-term deposits still use it precisely because both sides can verify the total owed with basic multiplication.
Where you'll actually encounter it
Simple interest shows up in short-term loans, some auto loans, and certain bonds where the issuer pays a fixed amount each period rather than letting interest snowball. Because the interest owed each year is identical, it's also easier to budget around than a compounding loan whose interest portion shrinks over time as the balance is paid down.
Worked example
Lend a friend 2,000 at 6% annual simple interest for 3 years. The calculation is 2,000 x 0.06 x 3 = 360 in total interest, so they'd owe 2,360 at the end, regardless of how the balance is structured along the way.
Compare that to the same 2,000 at 6% compounded annually for 3 years, which would grow to roughly 2,382 — a modest 22 difference over just three years that becomes far larger over longer terms or bigger principal amounts.
Simple interest and partial-year periods
When a loan or deposit runs for a fractional term, such as 90 days rather than a whole number of years, simple interest is usually calculated by converting the day count into a fraction of a year — for example, 90 divided by 365 — and multiplying that fraction into the same principal times rate formula, which keeps the daily accrual perfectly proportional.
A distinction worth double-checking
Before signing any agreement, confirm whether the lender is quoting simple or compound terms, since the two can produce noticeably different totals over multi-year periods — and remember this tool gives an estimate for comparison, not financial advice or a substitute for reading the actual loan contract in full.
When simple interest actually favors the borrower
Because simple interest never compounds, a borrower repaying a simple-interest loan slowly still owes exactly principal times rate times time — no snowballing penalty for taking longer, unlike a compounding loan where an extended term inflates the total owed. This is one reason some short-term personal loans and payday-style products advertise simple interest as a selling point, even though the headline rate itself may still be high.
People also search for
- simple interest calculator
- simple interest formula
- simple vs compound interest
- calculate interest on a loan
- short term loan interest
- simple interest example
- daily interest calculation
- fixed interest loan explained