Extra Mortgage Payment Calculator

On a standard 30-year mortgage, your monthly payment is fixed - but the split between principal and interest changes every single month. In the early years, the vast majority of each payment goes to interest. On a $400,000 loan at 6.5%, your first payment of around $2,528 is split roughly $2,167 in interest and just $361 in principal. By year 15, the split is more even. By year 28, almost all of it is principal.

This is why extra payments made early in the loan life have an outsized effect. When you pay an extra $500 in month 12, you eliminate that $500 from the balance - which means every subsequent month's interest is calculated on a lower number. That $500 doesn't just save you $500; it saves you every future interest charge that would have been calculated on it, which on a long loan at a high rate can be $1,500–$2,000 or more.

Extra payments in the final years of a loan save much less, because the balance is already small and most of each payment is already going to principal anyway.

Between 2020 and early 2022, the U.S. housing market experienced something genuinely unprecedented: a sustained period of 30-year fixed mortgage rates below 3%. The average rate bottomed out at 2.65% in January 2021 - the lowest ever recorded by Freddie Mac in over 50 years of data. Millions of homeowners moved quickly, either buying or refinancing, and locked in rates that looked impossibly cheap by any historical standard.

Then came 2022. The Federal Reserve began its most aggressive rate-hiking cycle since the early 1980s, and mortgage rates more than doubled in under two years - reaching 7.08% in October 2022 and briefly touching 8% in October 2023. Today, in 2026, the 30-year rate sits around 6.3%.

The result is what economists now call the rate lock-in effect - or more popularly, the golden handcuffs. Homeowners who secured a 2–3% rate are financially disincentivized from selling, because doing so means giving up that rate and taking on a new mortgage at double the cost. On a $500,000 mortgage at 3%, the monthly principal and interest payment is around $2,108. At 7%, that same loan costs $3,353/month - over $1,200 more every month, for the same house price. Nearly 82% of home shoppers surveyed said they felt "locked in" by their existing low-rate mortgage. Academic estimates suggest the lock-in effect reduced nationwide home sales by more than a million transactions and pushed home prices roughly 5–6% above where they otherwise would have been.

What this means for extra mortgage payments:

If you're in the golden handcuffs camp - holding a 2.5–4% mortgage - the calculus for making extra payments is genuinely different than it is for someone who bought at 6.5–7%.

At a 3% mortgage rate, every dollar of extra principal payment earns you a guaranteed, risk-free 3% return. A diversified stock portfolio has historically averaged 7% annually over long periods. That gap is large enough that, mathematically, investing the extra money rather than paying down a 3% mortgage is likely the better long-term financial decision for most people - especially in a tax-advantaged account like a 401(k) or IRA.

At a 6.5–7% mortgage rate, the math tilts the other way. Paying down the mortgage is a guaranteed return equal to your interest rate. The stock market may outperform that over decades, but it isn't guaranteed - and eliminating a 7% debt obligation is a risk-adjusted win that becomes increasingly hard to argue against.

The crossover point where most financial planners suggest switching from "invest first" to "pay down the mortgage" is generally around 5–6%, though your tax situation, investment account access, and risk tolerance all affect where your personal line falls.

The handcuffs are slowly coming off. As of early 2026, for the first time since 2020, the share of U.S. homeowners with mortgages at 6% or higher now exceeds those with mortgages below 3% - a sign that the lock-in effect is gradually easing as more recent buyers enter the market. Inventory levels began rising in 2024 and continued through 2025, and the U.S. housing shortage is approaching pre-pandemic norms in many markets. For anyone who bought or refinanced in 2022–2026, extra mortgage payments carry real financial weight - and this calculator shows exactly what they're worth.