Mortgage Amortization
Why is my mortgage
interest so high?
Your bank disclosed your interest rate. What they didn’t show you is what that rate means in year one, why extra payments may not save what you think, and how a mortgage recast can change the math entirely.
The federal government requires your lender to disclose your interest rate before you sign. That rate is accurate. What it doesn’t tell you is that in year one of a standard 30-year mortgage, roughly 85% of every payment disappears into interest before a single penny reduces what you owe. That is not a hidden fee. It is a mathematical consequence of how amortization works — and it is almost never explained at the closing table. This page includes a free mortgage recast calculator that shows exactly how a lump sum payment changes your trajectory, and why the timing of that payment matters more than most people realize.
Enter your mortgage details once below. Two calculators run simultaneously — the simplified view that most bank calculators show you, and the full picture that reveals what is actually happening to your money year by year.
What the bank is required to tell you
Federal law requires your lender to provide a Loan Estimate within three business days of your application. That document shows your interest rate, monthly payment, loan term, and estimated closing costs. It is regulated, standardized, and genuinely useful for comparing offers from different lenders.
Here is what federal law does not require your lender to show you: what that interest rate means in practice in year one. The Loan Estimate shows you the rate. It does not show you the amortization curve. It does not show you that on a 30-year mortgage, you will spend the majority of your loan term paying mostly interest before your balance meaningfully declines. That information exists — it is in your contract, in an amortization table that is rarely explained at closing — but no regulation requires your lender to walk you through it.
The federal mortgage disclosure framework was written with significant input from the banking and lending industry. The Truth in Lending Act, the Real Estate Settlement Procedures Act, and the Consumer Financial Protection Bureau’s Loan Estimate form were all shaped through a regulatory process in which lenders had substantial representation. The result is a disclosure regime that is technically transparent — every number is accurate — but strategically incomplete. It tells you what the rate is. It does not tell you what the rate does.
This is not an accusation. It is a description of how the system was built, by whom, and for whose benefit the design choices were made. Knowing this does not change your mortgage. It changes how you read the documents you sign.
The FTC’s own research confirmed this: Studies of actual mortgage borrowers found that both prime and subprime borrowers experienced significant misunderstandings about the terms of their recently obtained loans — even after spending considerable time shopping and comparing offers. Some learned the actual terms of their loan for the first time during a post-closing interview. The disclosures were technically compliant. They were not sufficient.
How amortization actually works
Amortization is the process of spreading loan payments over time so that each payment is equal. On a 30-year fixed mortgage, your monthly payment never changes. What changes, month by month, is how that payment is divided between interest and principal.
In the first month, you owe interest on the full loan balance. That interest is calculated at your annual rate divided by 12 — so on a $350,000 mortgage at 6.5%, month one interest is approximately $1,896. If your monthly payment is $2,213, only $317 goes toward reducing your balance. You paid $2,213 and your balance dropped by $317.
In month two, you owe slightly less interest because your balance is slightly lower. The split shifts imperceptibly toward principal. This continues for 360 months. The shift is so gradual in the early years that it feels invisible — because it is. Your balance barely moves for the first decade.
The rate is 6.5%. The year one reality is 85% interest. Both statements are true. Only one is shown at closing.
Why extra payments don’t always save what you think
This is the insight that changes how most homeowners think about their mortgage once they understand amortization.
A homeowner gets a raise. Feels financially responsible. Starts making an extra $200 payment each month. The mortgage servicer applies that extra payment to principal, which is correct. But without a recast, that extra principal payment eliminates months from the end of the loan — the payments in years 28, 29, and 30, which by that point are already almost entirely principal anyway. The interest savings on those eliminated payments is real, but modest.
Compare that to a lump sum principal payment in year three, followed by a formal mortgage recast. In year three, your amortization is still heavily front-loaded — the majority of every payment is still interest. Applying a lump sum to the principal when the balance is near its maximum, then recasting the loan to recalculate payments against the new lower balance, attacks the loan at the point of maximum interest leverage. The same dollars save significantly more because they are applied when the interest multiplier is highest.
What a mortgage recast is: A recast (also called a re-amortization) is when your lender recalculates your monthly payment based on your current remaining balance and remaining term. You make a lump sum principal payment — typically $5,000 minimum, though this varies by lender — and the lender recalculates your monthly payment downward. Unlike refinancing, there are no closing costs, no credit check, and no new loan. Most lenders charge a flat fee of $150 to $500. Call your servicer and ask: “Do you offer mortgage recasting, and what is the minimum lump sum required?”
The photograph analogy
A 6.5% interest rate is like a photograph taken of someone in mid-fall from a building. The photograph is real. The person in it is alive. The exposure is technically accurate. But the photograph does not show what happens next, and it does not show what happened before. Presented in isolation, it creates an impression that does not reflect the full truth of the situation.
A bank calculator that shows your monthly payment and your payoff date is technically accurate. It shows you real numbers from your real loan. What it does not show is the trajectory — the first decade of payments that barely move the balance, the crossover point where you finally start building equity faster than you are paying interest, the years of compound interest working against you before it works for you.
This is not fraud. It is framing. And framing, when consistently applied in one direction, produces outcomes that serve the institution more than the borrower.
What to actually do
Step 1 — Know your crossover point
The calculator above shows you the year when your principal payment first exceeds your interest payment. For most 30-year mortgages, this is somewhere between year 18 and year 23. Until that point, the majority of every payment goes to the lender as interest cost. Knowing this number changes how you think about every extra dollar you have available.
Step 2 — Apply extra principal early, not late
Extra principal payments save the most money when applied in the early years of the loan, when the amortization is most front-loaded. A $5,000 extra payment in year three saves dramatically more in total interest than the same $5,000 applied in year 20, because it reduces the balance at the point when the interest rate is being applied to its largest possible base.
Step 3 — Use a mortgage recast calculator before refinancing
If you have a lump sum available — tax refund, bonus, inheritance, sale of an asset — and your current rate is competitive, recasting is almost always cheaper than refinancing. No closing costs, no credit check, no resetting of the amortization clock on a new 30-year loan. Just a lower balance, a lower payment, and a faster path to the crossover point.
Step 4 — Call your servicer
Recasting is not automatically offered. You have to ask for it. Call the number on your mortgage statement and ask: “Do you offer mortgage recasting? What is the minimum lump sum required, and what is the fee?” Most major servicers offer it. Many borrowers never know to ask.
The redirected payment principle: When your mortgage is paid off — or when a recast lowers your payment — that freed cash does not disappear. It redirects to an investment account, where the same compounding math that worked against you in the early years of your mortgage now works for you. The Interest vs. Income calculator on this site shows you exactly how your interest burden changes as your mortgage balance declines.
Frequently asked questions about mortgage interest and amortization
Why is so much of my mortgage payment going to interest?
Because of how amortization works. Your monthly payment is calculated so that equal payments over the full loan term will retire the debt exactly at the end. In the early years, your balance is at its maximum, so the interest portion of each payment is also at its maximum. On a 30-year mortgage, roughly 80 to 87% of your first year’s payments go to interest depending on your rate. That percentage declines slowly over time as the balance drops.
When does my mortgage payment start going more to principal than interest?
The crossover point — when your principal payment first exceeds your interest payment — typically falls between year 18 and year 23 on a 30-year fixed mortgage, depending on your interest rate. The higher your rate, the later the crossover. The calculator above shows your specific crossover year. Until that point, the majority of every payment leaves your household as interest cost rather than building equity.
Do extra mortgage payments actually save money?
Yes — but the timing matters more than most people realize. Extra principal payments save the most when applied in the early years of the loan, when the amortization is most front-loaded. An extra $200 per month starting in year one saves significantly more in total interest than $200 per month starting in year 15, because early payments reduce the balance when interest is being calculated on its largest possible base. The calculator above shows you the exact dollar difference between extra payment scenarios.
What is a mortgage recast and how is it different from refinancing?
A mortgage recast is when you make a lump sum principal payment and ask your servicer to recalculate your monthly payment based on the new lower balance. Unlike refinancing, there is no credit check, no closing costs, no new loan, and no reset of your loan term. You keep your original interest rate and remaining term — your payment simply drops to reflect the lower balance. Most lenders charge a flat fee of $150 to $500. Recasting is almost always cheaper than refinancing when your current rate is competitive.
How much interest will I pay over the life of my mortgage?
On a $350,000 mortgage at 6.5% for 30 years, total interest paid is approximately $434,000 — more than the original loan amount. At 7%, that number rises to approximately $487,000. Most borrowers are aware that they will pay interest over time but have not calculated the total. The calculator above shows your specific total interest cost alongside the year-by-year breakdown of how that cost accumulates.
Why don’t banks explain amortization at closing?
Federal law requires lenders to disclose the interest rate, monthly payment, loan term, and closing costs. It does not require them to explain the amortization curve or show borrowers how their payments are divided between interest and principal year by year. The amortization schedule is available and is part of your loan documentation, but it is rarely presented or explained proactively. Research by the FTC found that many borrowers did not fully understand their loan terms even after closing — not because they were not given the information, but because the required disclosures did not make the practical implications clear.
What is a mortgage recast calculator and how do I use one?
A mortgage recast calculator shows you how a lump sum principal payment changes your monthly payment and total interest cost. Enter your current loan balance, interest rate, remaining term, and lump sum amount — the calculator shows your new monthly payment after the recast, total interest saved, and how the recast compares to making the same extra payment monthly instead. The calculator on this page does exactly that, including a year-by-year bar chart showing how the interest-to-principal split changes over the life of your loan.
Is it better to pay off my mortgage early or invest the extra money?
This depends on your interest rate relative to expected investment returns, your tax situation, and your personal risk tolerance. At mortgage rates above 6%, paying down principal often produces a guaranteed return that is difficult to beat consistently in the market on a risk-adjusted basis. At rates below 4%, the calculus often favors investing. This is a decision that benefits from personalized advice from a qualified financial professional who knows your full picture. The calculator on this site shows you the interest cost of your mortgage — use that number as one input in a broader conversation with an advisor.
About the Author
James is a certified financial coach and the founder of DebtInterestCalculator.com. Having bought and sold multiple homes, financed more than a few cars, and spent years wondering why the numbers never seemed to add up, he built this site to share what he wishes someone had shown him sooner. His mission is simple: help everyday people understand the real cost of borrowing — and the real power of knowing the rules.
For educational purposes only. Does not constitute financial or legal advice. Consult a qualified professional before making mortgage decisions.
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The Interest vs. Income calculator shows what percentage of your income currently goes to interest across all your obligations. Run it with and without your mortgage to see the full picture.