After 5 full years of mortgage payments, most homeowners have paid off less than 6% of their loan.
Not because they're doing anything wrong. It all comes down to how loan amortization works. Almost no one explains it clearly.
This isn't contrarianism. It's math. Once you see how your payment splits each month, three things become clear. Why your balance moves so slowly at first. Why extra payments help most in the early years. And exactly when you'll own your home outright.
TL;DR
- Loan amortization — each fixed payment covers both interest and principal, but the split between them shifts over time as your balance falls.
- On a $300,000, 30-year loan at 7%, your first $1,996 payment puts only $246 toward your balance — the other $1,750 goes to interest.
- The Two-Thirds Rule: roughly 67% of your total lifetime interest gets paid in the first half of a 30-year loan — which is why early extra payments have the biggest impact.
- Paying just $100 extra per month cuts payoff time by about 4 years and saves roughly $70,000 in interest on that same loan.
- By month 360 (your final payment), the same $1,996 payment puts $1,984 toward principal — almost the entire amount goes to your balance.
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See My Amortization Schedule — FreeWhat Is Loan Amortization?
Amortization means paying down a loan over time with regular payments.
Amortization
The process of reducing a loan balance over time through scheduled payments — each one covering both interest and a portion of what you originally borrowed. For example: a 30-year mortgage is amortized over 360 monthly payments, each one slightly shifting more money toward your balance and less toward interest.
Here's the key thing to understand: your monthly payment is fixed. But what's inside that payment changes every single month.
In month 1, most of your payment covers interest — the bank's fee for lending you money. Only a small slice reduces your actual balance. By month 360, almost all of your payment goes to your balance. You barely owe anything left.
Think of it like a seesaw. Interest starts high, principal starts low. Over 30 years, that seesaw slowly tips. By the end, most of each payment goes to principal. Almost none goes to interest.
The total payment stays the same. The split inside it changes each month.
How Each Payment Splits: The Math
Your lender isn't guessing at these numbers. Each payment uses the same formula.
Formula
Monthly Payment Formula: M = P × [r × (1 + r)^n] / [(1 + r)^n − 1]
Where: P = loan amount (what you borrowed) r = monthly interest rate (annual rate ÷ 12) n = total number of payments (years × 12)
On a $300,000 loan at 7% for 30 years: r = 7% ÷ 12 = 0.5833% per month n = 30 × 12 = 360 payments M = $1,996 per month (fixed for life of loan)
This example uses 7% to keep the math clean and consistent throughout. At today's 30-year fixed rate of 6.51% (Freddie Mac, May 22, 2026), that $300,000 loan costs $1,896 per month. The first payment splits as $1,625 to interest and $271 to principal. The pattern is the same. Only the dollar amounts change.
Once you know the monthly payment, the split for any given month works like this:
Formula
For any given payment: Interest portion = remaining balance × monthly rate Principal portion = monthly payment − interest portion New balance = old balance − principal portion
Month 1, worked example: Interest = $300,000 × 0.5833% = $1,750 Principal = $1,996 − $1,750 = $246 New balance = $300,000 − $246 = $299,754
That's month 1. You owed $300,000. You paid $1,996. Your balance dropped by $246.
In month 2, you owe $299,754 instead of $300,000 — so the interest charge falls by a dollar or two. The principal portion grows by that same amount. This keeps happening month after month — all 360 times.
Each month's interest is calculated fresh on whatever you still owe at that moment.
How the Split Changes Over 30 Years
Here's what that seesaw looks like at key moments in the life of a $300,000 loan at 7%.
| Payment | Interest | Principal | Balance Left |
|---|---|---|---|
| Month 1 | $1,750 | $246 | $299,754 |
| Month 60 (Year 5) | $1,647 | $349 | $282,402 |
| Month 120 (Year 10) | $1,502 | $494 | $257,449 |
| Month 180 (Year 15) | $1,295 | $701 | $222,040 |
| Month 240 (Year 20) | $1,003 | $993 | $171,917 |
| Month 300 (Year 25) | $588 | $1,408 | $100,752 |
| Month 360 (Year 30) | $12 | $1,984 | $0 |
Notice what's happening in the early years. After 5 full years of payments — 60 payments, $119,760 paid — your balance has only dropped from $300,000 to about $282,400.
That's a reduction of $17,600. Out of $119,760 paid. The other $102,160 went to interest.
The crossover point: Look at Month 240 in the table above — interest is $1,003 and principal is $993. That's the tipping point. Around Year 20 at 7%, your principal payment finally passes your interest charge. Before that, every single payment sends more money to your lender than to your own balance.
But watch what happens in year 25: each payment now puts $1,408 toward your balance. By year 30, it's $1,984 — nearly the entire payment. The curve accelerates sharply in the back half.
The key takeaway: Over 30 years, you'll pay roughly $418,560 in interest on a $300,000 loan. That's more than the home itself costs.
The Two-Thirds Rule: Your Mental Shortcut
You don't need to run the full schedule to understand where the interest goes.
Formula
The Two-Thirds Rule: On a 30-year mortgage, roughly two-thirds (about 67%) of your total lifetime interest is paid in the first half of the loan (years 1–15).
Examples at 7% annual rate: $200,000 loan → $279,000 total interest → ~$187,000 paid in years 1–15 $300,000 loan → $418,560 total interest → ~$281,000 paid in years 1–15 $400,000 loan → $558,000 total interest → ~$374,000 paid in years 1–15
Use this to understand: extra payments in years 1–10 have maximum impact, and refinancing in year 3 saves far more than refinancing in year 22.
Here's why: in the early years, almost every dollar you pay goes to interest. The bank collects most of its profit at the start. By year 20, most of the interest has been paid. Each payment now takes a real bite out of your balance.
This is why the first half of a mortgage is where your financial decisions matter most.
Why Extra Payments Are So Powerful
Here's what happens when you pay just a little more each month on that same $300,000 loan.
Every extra dollar you pay goes straight to your balance. It skips the interest charge entirely. That shrinks your balance faster, which means less interest charged in every subsequent month. This chain reaction compounds over the life of the loan.
| Extra Per Month | Payoff Time | Total Interest | You Save |
|---|---|---|---|
| $0 (standard) | 30 years | $418,560 | — |
| +$100/month | ~25.8 years | ~$349,000 | ~$70,000 |
| +$200/month | ~22.8 years | ~$302,000 | ~$117,000 |
Paying $100 more per month costs about the same as two dinners out. But it saves $70,000 in interest and cuts more than 4 years off your loan.
Early extra payments work so well because you cut interest that would have built up for decades. Every $100 you knock off your balance today stops earning interest for the next 20+ years. Small amounts early on have an outsized impact because of the Two-Thirds Rule.
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Run My Extra Payment Numbers — FreeWhat Amortization Means for Refinancing
Before you refinance, check your amortization schedule. The timing changes the numbers in a big way.
When you refinance, you reset your amortization schedule back to month 1 on a brand new loan. That means going back to paying mostly interest again.
Here's the scenario most people don't think through: say you're 10 years into a 30-year mortgage. By the Two-Thirds Rule, you've already paid about 67% of all the interest on your loan. If you take a new 30-year loan at that point, your total payoff time grows to 40 years. You also restart that front-loaded interest cycle from scratch.
Your monthly payment goes down. Your total interest paid could go up.
This doesn't mean refinancing is always wrong. If rates have dropped a lot, the lower payment can make up for the reset. If you refinance into a shorter term — say, 15 years — you build equity faster. You also pay less total interest, even if the rate stays about the same.
The rule of thumb: Always check the total interest on both loans — old and new — not just the new monthly payment. Our calculator shows you both numbers at once.
4 Steps to Use Amortization to Your Advantage
Here's what you can actually do starting this month.
1. Pull your full amortization schedule
Your lender is required to provide one at closing. Our calculator also builds your full schedule in seconds. See how each payment splits between interest and principal, month by month.
2. Add one extra payment per year
Add one extra payment per year — split into 1/12 extra each month. This cuts a 30-year loan by about 4–5 years and saves tens of thousands in interest. Ask your lender to mark it as a principal-only payment. That way, none of it goes toward future interest.
3. If you refinance, shorten the term
Consider a 15-year loan instead of another 30-year. Your monthly payment will be higher. But you pay far less interest over time — often hundreds of thousands less — and you build equity much faster.
4. Make extra payments early, not later
Thanks to the Two-Thirds Rule, extra payments in years 1–10 save the most. The same $100 extra in year 25 saves a small fraction of what it saves in year 3. If you have the capacity to pay more, start now.
What This Means for Your Loan
Your loan isn't designed to trick you. It's the math that makes fixed monthly payments work over a long term. But understanding how it works puts you in control.
The payment is fixed. The split isn't. And the split reveals exactly what your loan is costing you — and what you can do to change it.
Once you see your own schedule — the real numbers for your loan — the choice around extra payments and refinancing gets much clearer. That schedule takes about 30 seconds to generate.
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See My Full Amortization Schedule — FreeCommon Questions
Sources & Methodology
Monthly payment calculations use the standard amortization formula M = P × [r(1+r)^n] / [(1+r)^n − 1]. All examples assume a fixed-rate loan with monthly compounding and no additional fees (PMI, taxes, or insurance). Extra payment projections apply additional principal-only amounts to the standard amortization schedule each month. The Two-Thirds Rule reflects the proportion of total interest paid in months 1–180 on a 30-year loan at 7%, calculated as approximately 67%.
Sources: Consumer Financial Protection Bureau — Mortgage Key Terms: Amortization (CFPB), Federal Reserve Bank of St. Louis — 30-Year Fixed Rate Mortgage Average (FRED), Freddie Mac Primary Mortgage Market Survey. Note: 7% is used throughout as a worked example reflecting the approximate 30-year fixed average over recent years; as of May 22, 2026, the Freddie Mac PMMS 30-year fixed average is 6.51%.
Disclaimer: Results are for educational and informational purposes only. FiscalCalc is not a licensed financial advisor, mortgage broker, or tax professional. Consult a qualified professional before making major financial decisions.