A loan payment calculation tool estimates the fixed monthly payment needed to repay a loan over a chosen term, along with the total interest under the same assumptions. Enter the loan amount, annual percentage rate (APR), and term in years to see those estimates.
Formula
The calculator uses the standard fixed-payment loan formula. It first calculates a level payment from the principal, monthly interest rate, and number of monthly payments; the payment is rounded to the nearest cent. Total interest is then the sum of those rounded payments minus the amount borrowed.
- P = loan amount, in dollars.
- APR = annual percentage rate, entered as a percentage per year.
- r = monthly interest rate, calculated as APR ÷ 1,200. For an 8% APR, for example, r is 0.006667 per month.
- y = term in years.
- n = total number of monthly payments, calculated as y × 12.
- M = monthly payment, in dollars.
M = round(P × r ÷ [1 − (1 + r)−n], 2)
Total interest = M × n − P
This formula assumes a positive rate and equal payments made monthly. APR is divided by 12 to create the monthly rate; it is not entered as a decimal. The calculator’s APR limits are 0.01% to 100%, and its term limits are 0.0833 to 50 years. A zero-interest loan would use a different, simpler calculation: principal divided by the number of payments.
Worked Example
Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term—there are 5 × 12 = 60 monthly payments. The monthly rate is 8 ÷ 1,200 = 0.0066667.
- Substitute the values into the payment formula: M = round[20,000 × 0.0066667 ÷ (1 − (1.0066667)−60), 2].
- The unrounded payment is about $405.53, so the monthly payment rounded to cents is $405.53.
- Total of the rounded payments: $405.53 × 60 = $24,331.80.
- Estimated total interest: $24,331.80 − $20,000 = $4,331.80.
Because total interest uses the rounded monthly payment, it reflects the same cents-per-payment assumption as the result. A lender’s final schedule may differ slightly if it calculates interest by daily balances, adjusts the first or last payment, or applies a different rounding convention.
Assumptions
- The interest rate is fixed for the full term.
- Payments are equal, made monthly, and begin on a regular schedule.
- Interest compounds monthly at APR divided by 12.
- The calculation excludes fees, taxes, insurance, PMI, and escrow, because none are included as inputs.
When to Use a Loan Payment Calculator
Use this calculation to understand the payment and interest implied by a stated principal, APR, and term. It can also help you compare hypothetical scenarios by changing one input at a time—for instance, seeing how a longer term changes the monthly payment and total interest while holding the amount and rate constant. The result is arithmetic, not a statement about eligibility or whether a particular loan is appropriate.
Use figures that match the loan quote as closely as possible. The amount financed may differ from the amount received if costs are included in the balance. Confirm whether the quoted rate is an APR or a nominal interest rate, and whether the quoted payment includes only principal and interest or also other charges. Enter the rate as a percentage: type 8 for 8%, not 0.08.
How to Read the Results
The monthly payment is the modeled amount due for principal and interest under the level-payment formula. Early in a typical amortizing loan, more of each payment goes toward interest; as the balance declines, the interest portion generally falls and the principal portion rises. This does not mean each payment is divided into equal principal and interest amounts.
Total interest is the sum of the modeled payments minus the original principal. It is not the total cost of borrowing when fees or other charges apply. Nor is it the amount of interest that will necessarily appear on any particular statement: actual schedules can depend on payment dates, balance calculations, rounding, and contract terms.
Common Mistakes and Limits
- Mixing up APR and monthly rate: enter an annual percentage such as 8, not the monthly decimal. The formula converts APR to a monthly rate.
- Using the wrong term unit: this tool takes years, then multiplies by 12. A five-year term means 60 monthly payments.
- Assuming the payment includes everything: property-related charges, insurance, taxes, fees, and escrow are outside this calculation unless separately modeled.
- Expecting an adjustable-rate forecast: a single APR cannot model future rate changes. The estimate treats the entered APR as fixed.
- Overlooking rounding: the payment is rounded to cents before total interest is calculated. A real schedule can have a small adjustment, often in its final payment.
The formula is for a fully amortizing loan with equal monthly payments and a positive, unchanged rate. It does not calculate a variable-rate payment path, a balloon balance, an interest-only period, irregular payments, or the effect of extra payments. For those situations, the loan’s payment schedule and terms contain details this basic estimate does not represent.
Frequently Asked Questions
How do I calculate a monthly loan payment?
Convert APR to a monthly rate by dividing it by 1,200, and convert the term in years to months by multiplying by 12. Apply the fixed-payment formula shown above, then round the payment to cents.
Does APR mean the same thing as the interest rate?
Not always. APR is an annualized rate used for comparison and may reflect certain borrowing costs depending on how it is determined. This calculator uses the APR you enter as the rate for its monthly-payment formula; check the lender’s disclosure for the rate and cost details applicable to a specific offer.
Why is my lender’s payment different?
The lender may use a different financed amount, payment date, rate, compounding or balance method, rounding rule, or include charges not represented here. Compare the inputs and assumptions before treating two estimates as inconsistent.
Does a longer loan term lower the monthly payment?
For the same principal and positive fixed rate, spreading repayment across more monthly payments generally lowers the calculated payment, while increasing the amount of interest over the full term. The calculator shows the arithmetic for the inputs provided; it does not assess suitability.
Can I use this for a mortgage or car loan?
You can use it for the principal-and-interest portion when the loan has a fixed rate and equal monthly payments. It does not include housing costs, insurance, taxes, vehicle costs, fees, or other loan-specific charges.
This result is an estimate; the lender’s disclosure gives the exact figures.
Related
Formula used
in p | Loan amount | $ | 20000 | 1 | 100000000 in apr | Interest rate (APR) | % | 8 | 0.01 | 100 in yrs | Loan term | years | 5 | 0.0833 | 50 out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2 out int | Total interest | $ | pmt * yrs * 12 - p | 2
Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work
Method: the standard loan formula for this calculation, fixed rate and monthly compounding unless stated, rounded as each result states. Not financial advice; no lender, rate or product is recommended. See formulas and assumptions, the disclaimer or report an error.
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