Mortgage Calculator

Calculate your monthly mortgage payment, total interest, and view a full amortization schedule. Compare different loan terms and interest rates.

This calculator's Home Price input and its computed Loan Amount output happen to share the exact same internal key, but they are not the same number: the input is the purchase price you type in, while the output is that price minus Down Payment (line 11) — the actual amount financed. Home Price dominates Monthly P&I Payment: knock 10% off its default, then add 10% on top, and Monthly P&I Payment swings by about 25% across that range, ahead of Interest Rate (about 14%) and Loan Term (about 7%, and in the opposite direction). Annual Property Tax and Annual Insurance never move Monthly P&I Payment or the Loan Amount output at all — they're excluded from the core amortization formula (lines 19-22) and only get added in afterward to build Total Monthly Payment, this calculator's separate "all-in" figure (property tax and insurance together account for roughly 4% of Total Monthly Payment's sensitivity at these defaults). Down Payment moves Loan Amount down one-for-one in the expected direction, but its ±10% span is a smaller relative share (about 5% of Loan Amount) than Home Price's span, simply because the default down payment ($70,000) is a smaller slice of the $350,000 purchase than the price itself. The underlying loop computes a balance for every month of the full loan term, but only the first 360 months (30 years) are ever pushed into the stored schedule array (line 38) — months beyond that are computed and discarded, never stored anywhere. The yearly chart data is built by slicing that same capped schedule array (line 54), so a Loan Term longer than 30 years drops its later years from both the table AND the chart entirely; nothing "summarizes" them. This calculator does not account for PMI, HOA fees, or closing costs — it is principal, interest, tax, and insurance only.