Guide
How Loan Payments Work
Fixed loan payments are based on loan amount, interest rate, term, and payment schedule. The monthly payment is designed to repay both principal and interest over the loan term.
The Main Inputs
A fixed-rate loan payment depends on principal, annual interest rate, and term. The calculator converts the annual rate into a monthly rate and the term into monthly payments.
The payment is calculated so the loan balance reaches zero at the end of the scheduled term, assuming payments are made as modeled.
- Principal is the amount borrowed.
- Interest rate is the borrowing cost stated as an annual percentage.
- Term is the length of repayment.
- Monthly payment is the scheduled principal-and-interest payment.
Total Paid and Total Interest
Total paid is monthly payment multiplied by the number of payments. Total interest is total paid minus principal.
Longer terms often lower the monthly payment but increase total interest because the balance remains outstanding for more months.
What the Simple Calculator Does Not Include
A basic payment estimate usually excludes taxes, insurance, escrow, origination fees, late fees, prepayment penalties, and variable-rate changes.
For auto or personal loans, use product-specific calculators when the inputs or caveats are different.
Loan Payment Logic
Monthly rate
Monthly Rate = Annual Rate / 12
The annual rate is converted into a monthly rate before payment math is applied.
Payment count
Number of Payments = Years x 12
A 5-year loan has 60 monthly payments; a 30-year loan has 360.
Fixed payment
Payment = P x [r(1+r)^n] / [(1+r)^n - 1]
P is principal, r is monthly rate, and n is the number of payments.
Worked Examples
$20,000 loan at 8% for 5 years
- Input
- $20,000 principal, 8% annual rate, 5-year term
- Formula
- P = 20,000, r = 0.08 / 12, n = 60
- Output
- $405.53 monthly payment
The scheduled payments total about $24,331.67, including about $4,331.67 of interest.
$30,000 auto loan at 6.9% for 5 years
- Input
- $30,000 loan amount, 6.9% annual rate, 5-year term
- Formula
- P = 30,000, r = 0.069 / 12, n = 60
- Output
- $592.62 monthly payment
Auto loan estimates may still exclude taxes, title, registration, insurance, and dealer fees.
$15,000 loan at 0% for 5 years
- Input
- $15,000 principal, 0% annual rate, 5-year term
- Formula
- $15,000 / 60
- Output
- $250.00 monthly payment
At zero interest, the payment is just principal divided by the payment count.
Frequently Asked Questions
What determines a loan payment?
The main inputs are loan amount, interest rate, repayment term, and payment frequency.
Why does a longer term lower the monthly payment?
A longer term spreads repayment across more payments. The tradeoff is often higher total interest.
What is total interest?
Total interest is total paid over the loan term minus the original principal.
Does the calculator include taxes or insurance?
No. Basic loan payment calculators estimate principal and interest only unless other costs are included in the loan amount.
What happens at 0% interest?
The payment is principal divided by the number of payments because no interest accrues.
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