Mortgage Calculator
Estimate a mortgage's monthly principal & interest, and see how adding an extra monthly payment shortens the term and cuts total interest.
Principal, interest, and the power of extra payments
A mortgage is a large amortized loan: the base monthly payment of principal and interest stays level, while the split shifts from mostly interest to mostly principal over the years. This tool computes that base payment and, if you add an extra amount each month, simulates the loan month by month to find the real payoff date.
Every extra dollar goes straight to principal, so it removes all the future interest that dollar would have accrued. Because that effect compounds over decades, even a modest extra payment can shave years off a 30-year term and save a large sum in interest — the tool shows both.
This estimate is principal and interest only. It excludes property taxes, homeowners and mortgage insurance, HOA dues, and closing costs, which together can add substantially to the true monthly outlay. It also assumes a fixed rate. Use it to compare scenarios, not as a loan quote.
Sources: CFPB — How paying down a mortgage works, CFPB — Loan options
Frequently asked questions
What does “P&I” mean?
Principal and interest — the portion of a mortgage payment that repays the loan itself. Your actual monthly bill usually also includes taxes and insurance, often collected in an escrow account.
How does an extra payment save so much?
It reduces the balance ahead of schedule, so interest stops accruing on that amount for the rest of the term. Over a long mortgage the avoided interest compounds, which is why small regular extras have an outsized effect.
Does this include taxes and insurance?
No — only principal and interest. Property tax, homeowners insurance, and (if applicable) mortgage insurance are additional and vary by location and lender.
Should I pay extra or invest instead?
That depends on your rate, taxes, and goals, and this tool can't decide it for you. It only shows the interest math of paying extra — weigh it against other options with a professional.
