How do I find the biggest loan a set monthly payment can afford?

Fix the payment you're comfortable with along with the rate and term, and solve for the loan amount — it's the same annuity formula a standard loan calculator uses, run in reverse. This calculator does that solve directly instead of making you guess an amount and check the payment it produces.

Can this tell me the interest rate on a loan I already have?

Yes, if you know the amount, the payment, and the term. There's no closed-form formula for rate, so this searches for the rate that makes those three numbers consistent, the same way a spreadsheet's RATE function does.

How is solving for term different from solving for payment?

Solving for payment answers "what will I owe each month"; solving for term answers "how long until this is paid off" for a payment you've already fixed. Both start from the same three remaining knowns — this tool lets you pick which one is unknown instead of assuming it's always the payment.

Calculator

Payment Calculator

Every loan calculator assumes you already know the amount, the rate, and the term, and just want the payment. This one solves in any direction: fix the payment you can afford and find the amount it buys, the term it takes, or the rate it implies — the same annuity formula run backward, with a numerical solve for the rate since it has no closed form.

Results

Solve for

Loan amountMonthly paymentInterest rateLoan term

Enter a loan amount greater than zero.

Loan

Loan amount

Monthly payment

—Solving

Rate & term

Interest rate

Loan term

years

months

How this is calculated

For educational purposes only. Results are estimates and do not constitute financial, tax, or legal advice. Consult a qualified professional before making any financial decisions.

How to use it

Pick which of the four numbers you don't know with the Solve for toggle above the results — that field locks and shows the answer once the other three are filled in.

Know the payment you can afford? Solve for loan amount to see the biggest loan it buys. Curious how long a fixed payment takes to pay off a balance? Solve for loan term instead.

Solving for the interest rate is useful for sanity-checking a loan you already have — enter the amount, payment, and term from your statement and see what rate they imply.

Assumptions

Assumes a fixed-rate, level-payment installment loan — the same math behind a mortgage, auto loan, personal loan, or student loan, with interest applied monthly (the nominal annual rate ÷ 12).
Solving for the interest rate has no closed-form formula, so this searches numerically for the rate that makes your amount, payment, and term agree — the same approach a spreadsheet's RATE function uses.
Solving for loan term can land on a fractional number of payments — since a payment can't be split across a partial month, this rounds up to the next whole month and shows the payment that whole term actually implies, which may differ slightly from what you typed in.
Doesn't account for taxes, insurance, fees, or extra payments.

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