Play · amortization, and an honest trade-off
Mortgage Payoff Accelerator
Updated 2026-07-30 · Sources: 4 · Concept: extra principal, and when it is not the best use of the dollar
Every dollar of extra principal skips the interest that dollar would otherwise have paid for the rest of the loan, which is why an amount that looks trivial next to the balance can move the payoff date by years. This tool draws that. It also does the thing the payoff calculators built to sell you a debt-free celebration usually leave out: it compares the extra payment against investing the same money, tells you exactly where the crossover sits, and does not pretend the answer is obvious.
Predict first
A $280,000 balance at 6.5%, 28 years left to run. Pay an extra $200 a month, every month, until it is gone. How much interest does that save over the life of the loan?
Pick an estimate, or skip to your own numbers.
The trade-off nobody puts on the calculator
Paying extra principal is an investment, and its return is exactly your mortgage rate, guaranteed and tax-free at the point of payment. Investing the same money instead has a higher expected return and no guarantee at all. So the arithmetic has one clean answer and the decision does not.
Why the guaranteed return keeps winning anyway, for a lot of people. The comparison above assumes you actually invest the money, every month, for decades, and do not sell in a bad year, and it ignores tax in both directions. A paid-off house is also a lowered floor: the smallest number your household can survive on drops, which changes what job you can leave, what illness you can absorb, and what you can give. Scripture does not forbid a mortgage and does not command paying it off early; it treats debt soberly as a relationship of servitude to the lender and tells you to keep your word about it. If the guaranteed return plus a shorter leash is worth more to you than the expected extra from investing, that is a defensible answer, not a mathematical error, and so is the reverse. See debt, borrowing and surety.
Method: a standard fixed-rate amortization computed month by month in this page: payment M = P·r(1+r)n/((1+r)n−1), where r is the annual rate ÷ 12 and n is the months remaining. Interest accrues on the outstanding balance each month; the extra payment is applied entirely to principal, and the final month is trimmed to the balance actually left. Formula check: $280,000 at 6.5% over a full 30 years gives $1,769.79 a month, the same figure the rent-vs-buy tool uses and the standard published result for those inputs. Defaults: 6.5% is close to Freddie Mac's Primary Mortgage Market Survey 30-year fixed average of 6.58% for the week of 23 July 2026 (freddiemac.com/pmms); the balance and years remaining are illustrative round numbers for a loan a few years in; 8% is a deliberately modest stand-in for long-run stock returns, not a promise (investor.gov). What this leaves out: tax, in both directions: mortgage interest is deductible only if you itemize, and most households take the standard deduction (IRS Topic 505), while investment gains are taxed unless they sit in a retirement account. It also leaves out an employer match, which beats both options outright, and the emergency fund that should exist before either. Confirm with your servicer that extra payments are applied to principal and do not simply pre-pay the next installment. This is a teaching model, not advice.
Owe no man any thing, but to love one anotherRomans 13:8
KJV, quoting only the clause verified against the text; the verse continues 'for he that loveth another hath fulfilled the law.' Paul is finishing a passage about paying what you owe (taxes, custom, fear, honour) and pivots to the one debt that is never discharged. Read as a flat ban on mortgages it proves too much; read as Paul wrote it, it makes an unpaid obligation something to settle rather than to carry comfortably.