The Front-Loaded Interest Problem
When you take out a 30-year mortgage, your monthly payment stays the same for the life of the loan. But where that payment goes changes dramatically over time.
In the first year of a $300,000 loan at 6.75%, roughly $1,688 of your $1,946 monthly payment goes to interest. Only $258 goes toward actually paying down your loan. That means 87% of every payment is the cost of borrowing — not building equity.
By year 15, the split is roughly 50/50. By year 25, most of your payment is finally going to principal.
Why It Works This Way
Interest is calculated on your remaining balance, not your original loan amount. In month 1, you owe $300,000, so you pay interest on $300,000. In month 200, you might owe $180,000, so you pay interest on a much smaller number.
The math is straightforward:
As your balance shrinks, the interest portion shrinks, and more of your fixed payment goes to principal. This creates the classic amortization curve — slow equity building at first, accelerating over time.
What This Means for You
If you plan to sell or refinance within 5-7 years, you will have paid mostly interest and built relatively little equity from payments alone. Home appreciation may be your primary equity source in that period.
Extra payments are disproportionately powerful early in the loan because they reduce the balance that interest is calculated on for every remaining month. A $200/month extra payment in year 1 saves far more total interest than the same payment starting in year 15.
See It In Action
Open the Mortgage Modeler and watch the Payment Chart — the blue (principal) and red (interest) lines cross around year 18-20 on a typical 30-year loan. That crossover point is when you start paying more principal than interest each month.
Try adding an extra payment and watch the crossover move earlier. That visual shift represents real money saved.