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Simple Interest Calculator
Simple interest is charged only on the original principal, never on interest already accrued. Enter the principal, the annual rate and the time in years, months or days to get the interest and the total amount due.
- Total (principal + interest)
- $5,900.00
- Interest per day
- $0.82
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Enter the principal — the amount lent or borrowed.
- Enter the yearly interest rate.
- Enter the length of time and choose years, months or days.
Worked examples
$5,000 at 6% for 3 years
- Simple interest
- $900.00
- Total (principal + interest)
- $5,900.00
- Interest per day
- $0.82
$2,000 at 9% for 18 months
- Simple interest
- $270.00
- Total (principal + interest)
- $2,270.00
$10,000 at 8% for 90 days
- Simple interest
- $197.26
- Total (principal + interest)
- $10,197.26
- Interest per day
- $2.19
Where simple interest is used
Most car loans and many personal loans accrue simple interest daily on the outstanding balance. Short-term notes, loans between family members and late-payment interest on invoices are also usually simple.
Savings accounts, credit cards and investments compound instead, so use the compound interest calculator for those.
Day-count conventions
This calculator uses a 365-day year. Some commercial loans and money-market instruments use a 360-day year, which makes each day’s interest slightly larger: divide by 360 instead of 365 if your contract says so.
Questions people ask
What is the simple interest on $5,000 at 6% for 3 years?
$900. 5,000 × 0.06 × 3 = 900, so the total due is $5,900.
How do I calculate interest for a number of days?
Multiply principal × rate × days ÷ 365. $10,000 at 8% for 90 days is 10,000 × 0.08 × 90 ÷ 365 = $197.26.
What is the difference between simple and compound interest?
Simple interest is the same every period. Compound interest grows because each period’s interest is added to the base. $8,000 at 7% for 4 years earns $2,240 simple or $2,486.37 compounded annually.