Loan Calculator
Calculate the monthly payment and total interest for any fixed-rate amortized loan — auto, personal, or student. Enter the loan amount, interest rate, and term in years.
Loan payment
Example: $25,000 at 7% for 5 years ≈ $495.03/month.
Companion guide: How the monthly payment formula works derives the formula this calculator runs — monthly compounding, the term in months, and what changes with rate and term — on a fictional loan. This page covers how the loan calculator applies it: the three inputs it takes, the month-by-month schedule behind the total-interest line, and how to read the result. Every explainer on the site is listed under Guides.
How an amortized loan works
A fixed-rate loan is repaid with equal monthly payments that cover the interest owed plus a slice of principal. In the worked example — a fictional $25,000 borrowed at 7% over 5 years — the payment is $495.03 a month, and you repay $29,702 in all, of which $4,702 is interest. The calculator takes exactly three inputs — the amount, the annual interest rate, and the term in years — and has no loan-type setting: an auto loan, a personal loan, and a student loan with the same three figures produce the same payment, because the arithmetic is the same. Example B makes the point with different fictional figures: $12,000 at 9.5% over 3 years comes to $384.40 a month and $1,838 of interest across 36 payments. Every figure on this page is computed when the page is built by the same tested engine that powers the calculator above; the rates and amounts in the examples are illustrative inputs chosen for the arithmetic, not quotes.
What the engine computes, step by step
The form hands your three inputs to one engine function, which validates them, runs the steps below in order, and returns a typed result — or an explicit, human-readable error if an input cannot be used. The interface only formats what comes back; it never does arithmetic of its own.
- Validation. The amount must be greater than zero, the rate cannot be negative, and the term must be a positive number of years; each input also has an upper bound. A value that fails is refused before any arithmetic runs, with the engine's own message — the messages are quoted in the FAQ below.
- Monthly rate = the annual rate ÷ 12. This is the engine's compounding convention: the standard amortized-loan (PMT) formula with monthly compounding, the convention behind US mortgages and most consumer loans. At 7% the monthly rate is 0.5833%.
- Number of payments = years × 12, rounded to a whole month: 60 in Example A. A term of 2.5 years becomes 30 payments.
- The fixed payment is the one amount that, paid every month at that monthly rate, retires the balance exactly at the last payment — $495.03 here. The companion guide derives the formula.
- The schedule is then computed one month at a time: each month the engine charges interest on the balance still outstanding — balance × the monthly rate — and the remainder of the fixed payment reduces the principal. Running the schedule rather than relying on a closed-form total is what makes extra payments and payoff dates exact.
- Totals. Total interest is the sum of every month's interest charge, and the total of payments is the loan amount plus that interest: $4,702 and $29,702 in Example A.
| Year | Interest paid | Principal paid | Balance at year end |
|---|---|---|---|
| 1 | $1,612.91 | $4,327.45 | $20,672.55 |
| 2 | $1,300.08 | $4,640.28 | $16,032.27 |
| 3 | $964.63 | $4,975.73 | $11,056.54 |
| 4 | $604.94 | $5,335.42 | $5,721.12 |
| 5 | $219.24 | $5,721.12 | $0.00 |
| Whole term | $4,701.80 | $25,000.00 | — |
Month one, and how the split moves
In month one of Example A the balance is the whole $25,000, so interest is $25,000 × 0.5833% = $145.83, and the remaining $349.20 of the $495.03 payment reduces the principal: 29.5% of the first payment is interest. Because the balance falls every month, the interest charge falls with it and the principal share grows. The table shows year 1 paying $1,613 of interest against $4,327 of principal, and year 5 paying $219 against $5,721.
In Example A — 60 payments at 7% — the principal share exceeds the interest share from the very first month; how much of an early payment is interest depends on the rate and on how long the balance stays large. The methodology page's reference loan — $200,000 at 6% over 30 years, 360 payments — shows the other extreme: its first month charges $1,000.00 of interest against $199.10 of principal, so 83.4% of that payment is interest, because a 360-month schedule keeps the balance near its starting point for years. Nothing is front-loaded by anyone; the interest charge simply follows the balance, and the balance falls slowly when the term is long.
What changes with the rate and the term
The amount scales the result in proportion — double the amount and both the payment and the total interest double — so the two inputs that reshape a loan are the rate and the term. The table holds Example A's $25,000 fixed and recomputes the payment and the total interest across 5 illustrative rates and 3 terms. Every cell is an engine output.
| Rate | 3 years (36 payments) | 5 years (60 payments) | 7 years (84 payments) |
|---|---|---|---|
| 4% | $738.10 / $1,572 | $460.41 / $2,625 | $341.72 / $3,704 |
| 5.5% | $754.90 / $2,176 | $477.53 / $3,652 | $359.25 / $5,177 |
| 7% | $771.93 / $2,789 | $495.03 / $4,702 | $377.32 / $6,695 |
| 8.5% | $789.19 / $3,411 | $512.91 / $5,775 | $395.91 / $8,257 |
| 10% | $806.68 / $4,040 | $531.18 / $6,871 | $415.03 / $9,862 |
Reading down a column: at a fixed 5-year term, moving the rate from 4% to 10% raises the payment from $460.41 to $531.18 and the total interest from $2,625 to $6,871. Reading across a row: at 7%, stretching the term from 3 to 7 years lowers the payment from $771.93 to $377.32 while raising the total interest from $2,789 to $6,695 — $3,905 more for the lower payment, because the balance is outstanding, and charged interest, for 48 additional months. The engine compares; whether a lower payment over more months or a higher payment over fewer fits a budget is not a question the arithmetic answers.
Two conventions worth knowing
A 0% rate divides the principal evenly across the term. The payment formula divides by the rate, so the engine handles zero as a separate case: Example A at 0% is $25,000 ÷ 60 = $416.67 a month, with $0 of interest and a total of payments equal to the amount borrowed. The displayed payment is the rounded view of a more precise internal value, which is why 60 × $416.67 does not land exactly on $25,000; internally nothing is rounded between steps.
The term is converted to whole months. The form takes years, and years × 12 is rounded to the nearest month before the formula runs. A term of 2.5 years is therefore 30 payments — $910.80 a month on Example A's amount and rate, with $2,324 of interest — and a term that does not land on a whole month is rounded to the nearest one.
The reference figure, recomputed
The methodology page names the figure the engine is validated against: a $200,000 loan at 6% over 30 years. Recomputed here when the page is built, the same function that runs this calculator returns a payment of $1,199.10 and total interest of $231,676, matching the figures the methodology page and the automated tests expect. That is the point of computing the copy rather than typing it: if the copy and the code ever disagreed, the site would fail to build rather than publish inconsistent numbers.
The rate this calculator takes
The rate field is the loan's interest rate — the note rate the payment is computed from. It is not an APR. Where a loan carries upfront fees, the APR Calculator runs a different engine function: it computes the payment on the full principal at the note rate, treats the amount actually received as the principal minus the fees, and solves for the annual rate that discounts those payments back to the net amount received. With fees greater than zero that rate is at or above the note rate; with no fees the two coincide. The Fee-adjusted APR explained guide works through it. This page has no fee input, so a figure typed into the rate field is treated as the note rate, whatever it was called on the paperwork.
How to read the result
- The large "/ month" figure is the fixed principal-and-interest payment, shown to the cent — $495.03 in Example A. It is the only per-month line, because this calculator has no tax, insurance, or fee inputs.
- Total interest is the sum of every month's interest charge from the schedule, shown in whole dollars — $4,702 in Example A.
- Total of payments is the loan amount plus the total interest — $29,702 in Example A. On a schedule that runs its full term it agrees to the cent with the payment multiplied by the number of payments ($29,701.80 here); the engine reports the schedule's sum rather than the product.
- Copy result places a one-line summary — the payment per month and the total interest — on your clipboard. Reset clears the three fields and returns the result box to its placeholder.
The result updates as you type. While any field is blank the box shows its placeholder; a field that cannot be read as a number is flagged with a message beneath it, and the box asks you to fix it before a payment is shown. Money is shown to the cent, or to whole dollars for large totals like lifetime interest; internally every calculation keeps the full precision of IEEE-754 double-precision arithmetic, and nothing is rounded between steps. Your lender's figure may differ by a few cents depending on their rounding and day-count conventions — the difference is presentational, not an error.
Where the calculator stops
The limits are the engine's, and the methodology page states them. The calculators model fixed-rate, fully amortizing loans. They do not model adjustable-rate mortgages, interest-only periods, balloon payments, or negative amortization: whatever rate you enter is held fixed for every month of the term. Revolving balances follow different arithmetic, which the Credit Card Payoff Calculator runs. There is no extra-payment field on this form; the engine's schedule can take a fixed extra principal payment each month, and the Mortgage Payoff Calculator runs the with-and-without-extra comparison — on Example A, an illustrative $100 a month of extra principal would shorten the schedule to 49 payments and lower the total interest by $939, figures the engine reports for comparison, not as a recommendation. There are no fee, tax, or insurance inputs, so the total of payments is principal and interest only, and the engine does not know your lender's day-count or rounding conventions, fees, or prepayment terms. Inputs are validated before any arithmetic runs: non-numeric, negative, infinite, or out-of-range values return a plain-language error instead of a number. And a correct calculation can still be the wrong calculation for your situation — choosing the right loan for a real-world decision is judgment we cannot automate.
Frequently asked questions
What kinds of loans does this cover?
Any fixed-rate, fully amortizing loan with equal monthly payments — car loans, personal loans, student loans, and home-equity loans all work the same way. It does not model interest-only loans, credit-card revolving balances, or variable-rate loans.
What is the difference between the interest rate and APR?
This calculator takes the interest rate — the note rate the payment is computed from — and has no fee input. The APR Calculator on this site runs a different engine function: it computes the payment on the full principal at the note rate, treats the amount actually received as the principal minus the fees, and solves for the annual rate that discounts those payments back to the net amount received. With fees greater than zero that APR is at or above the note rate; with no fees the two coincide.
What determines the total interest?
Three inputs and nothing else: the amount, the rate, and the term. The amount scales the interest in proportion. At a fixed 5-year term on $25,000, moving the rate from 4% to 10% raises total interest from $2,625 to $6,871; at a fixed 7%, stretching the term from 3 to 7 years raises it from $2,789 to $6,695 while lowering the monthly payment. The engine's schedule also accepts a fixed extra principal payment each month, which this form does not expose; the Mortgage Payoff Calculator runs that comparison.
Is the monthly payment fixed?
For a fixed-rate loan, yes — the principal-and-interest payment is the same every month for the whole term, even though the split between principal and interest shifts over time.
What happens if I enter 0% as the rate?
The engine divides the principal evenly across the term instead of running the payment formula, which would divide by zero. On $25,000 over 60 months the payment is $416.67, total interest is $0, and the total of payments equals the amount borrowed.
Can I enter the term in months?
The field takes years, and a fraction works: years × 12 is rounded to the nearest whole month before the formula runs, so 2.5 years is 30 payments — $910.80 a month on Example A's amount and rate. For a term quoted in months, divide by 12 and enter the result.
Which inputs does the calculator refuse?
Each input is validated before any arithmetic runs, and the engine returns its own message rather than a number. An amount of zero: "The loan amount must be greater than 0." A negative rate: "The interest rate cannot be negative." A rate above the engine's ceiling: "Enter an interest rate below 100%." A zero (or negative) term: "Enter a loan term in years." A term beyond the engine's limit: "Terms are limited to 60 years." A value that cannot be read as a number is flagged on the field itself before the engine is called.
Why might my lender's payment differ from the calculator by a few cents?
Internally the engine keeps the full precision of IEEE-754 double-precision arithmetic and rounds only on screen, to the cent (or to whole dollars for large totals like lifetime interest). Your lender's figure may differ by a few cents depending on their rounding and day-count conventions — the difference is presentational, not an error.
Not financial advice: a general educational estimate. Actual terms depend on your lender and credit. Values are processed locally in your browser and never transmitted. See the methodology page.