Every fixed loan connects three numbers: how much you borrow, how long you take to pay it back, and how much you pay each month. Know any two, and the third is fixed by the math — which means you can work the formula in whichever direction actually answers your question.
The Three Numbers That Define Any Loan
- Loan amount — how much you're borrowing
- Interest rate — the cost of borrowing, expressed annually
- Term — how many months you have to pay it back
Given the loan amount, rate, and term, there's exactly one monthly payment that pays the loan off precisely on schedule — that's the most common question, and the most common calculation.
Working the Formula Backward
Sometimes the question runs the other direction. "I can afford $400 a month — how much can I actually borrow?" flips the same formula around to solve for loan amount instead of payment. "I want to pay $400/month on a $20,000 loan — how long will that take?" solves for term instead.
Why This Matters for Budgeting
Most people start from "what can I afford per month" rather than "how much do I want to borrow." Solving for loan amount given a target payment answers the actually useful question directly, instead of guessing at loan amounts and checking whether the resulting payment fits your budget.
Step-by-Step: Solve for Any of the Three
- Choose which value you want to solve for: payment, loan amount, or term
- Enter the two values you already know
- Get the missing value calculated instantly