Loan Size Calculator

Most borrowers think about loan size first and discover their monthly payment later — but lenders work backward from your payment capacity to determine loan approval. Your monthly budget is the constraint that determines everything else.

The calculation uses present value of annuity mathematics. Your loan amount is the present value of all future payments, discounted by the interest rate. Higher rates mean each dollar of payment supports less loan principal, while longer terms spread the same principal across more payments, reducing each individual payment.

This tool assumes standard amortization where each payment covers interest first, then principal. Early payments are mostly interest — by month 360 of a 30-year loan, you have paid roughly $185,000 in interest on a $300,000 loan at 6.5% rates.

Use this calculator when house hunting with a firm monthly budget, comparing auto loan options within payment limits, or evaluating investment property cash flow requirements. It answers 'how much can I borrow' when you know your payment comfort zone.

Do not use this for variable-rate loans where payments change over time, lines of credit with flexible payment schedules, or business loans with seasonal payment structures. The calculation assumes consistent monthly payments — it breaks down when payment amounts vary by design.

This tool works best before you shop for specific properties or vehicles. Once you find a target purchase, switch to a standard loan calculator to verify the monthly payment fits your budget.

Borrowers often confuse maximum loan amount with smart loan amount. The calculator shows what you can qualify for, not what you should borrow. Using the full amount leaves no room for rate increases, income drops, or emergency expenses.

Another common error is ignoring total cost focus. A $300,000 loan at 6.5% for 30 years costs $455,000 total — $155,000 in interest. Many borrowers see the monthly payment fits their budget without calculating the lifetime cost. A 15-year term at the same rate costs only $105,000 in interest, saving $50,000 despite higher monthly payments.

Users also mistake rate shopping impact. Each 0.25% rate reduction increases borrowing power by roughly $12,000 on a $300,000 loan. Shopping for better rates can increase your home budget more than saving additional down payment money.

The loan amount formula is PV = PMT × [(1 - (1 + r)^-n) / r], where PV is loan amount, PMT is monthly payment, r is monthly interest rate, and n is number of payments. This present value calculation determines how much principal your payment stream can support.

For example, a $2,000 monthly payment at 6% annual rate (0.5% monthly) for 30 years (360 payments): PV = 2000 × [(1 - (1.005)^-360) / 0.005] = $333,061. The denominator (1.005)^-360 equals 0.1661, so the bracket equals 166.79, yielding a $333,582 loan amount.

As rates increase, loan capacity drops exponentially. At 8% instead of 6%, the same $2,000 payment supports only $272,686 — a $60,000 reduction for just 2% higher rate. The effect accelerates at higher rates because more of each payment goes to interest rather than principal reduction.

Loan officers use debt-to-income ratios to qualify borrowers, but the maximum qualifying payment differs from the optimal payment. Most lenders allow up to 36-43% total debt-to-income, but borrowers who stay below 28% housing-only ratios get better rates and terms. The calculator shows mathematical maximum — underwriting adds income verification, credit score adjustments, and reserve requirements that reduce actual approval amounts.