How much total interest will I pay on a $400,000 mortgage?

On a $320,000 loan (after 20% down on a $400,000 home) at 6.75% for 30 years, you will pay approximately $459,000 in total interest — more than the loan itself. Shorter terms dramatically reduce this figure.

What is the interest-to-principal ratio on a mortgage?

The interest-to-principal ratio shows how much interest you pay for every dollar of principal. At 7% for 30 years, you pay about $1.39 in interest for every $1 borrowed. The ratio drops significantly with higher down payments, lower rates, or shorter terms.

Why do I pay so much interest in the early years of my mortgage?

Mortgage interest is calculated on the remaining balance. In year 1, almost the entire loan balance accrues interest. Over time, as you pay down principal, the interest portion shrinks. In the first 5 years of a 30-year mortgage, typically 80–85% of each payment goes to interest.

How does the mortgage interest tax deduction work?

You can deduct mortgage interest on loans up to $750,000 if you itemize deductions. The benefit only applies when your itemized deductions (interest + property tax + other) exceed the standard deduction ($14,600 single / $29,200 married for 2024). Many homeowners no longer benefit since the standard deduction was doubled in 2018.

Does inflation reduce the real cost of mortgage interest?

Yes. Your mortgage payment is fixed in nominal dollars, but inflation erodes its real purchasing power over time. At 2.5% annual inflation, a $2,000/month payment in year 30 has the same real value as about $960 today. This is one reason fixed-rate mortgages are considered a hedge against inflation.

Mortgage Interest Calculator

Find out exactly how much total interest you will pay — and how rate, term, and inflation change the picture.

Home Price

Down Payment

Interest Rate

Loan Term

Total Interest Paid

$427,185

Over 30 years on a $320,000 loan

Principal: $320,000

Total Interest: $427,185

Monthly Payment

$2,076

Interest-to-Principal Ratio

133%

Effective Home Cost

$827,185

Interest — First Half

$288,138

Advanced

Interest Deep Dive

Year-by-year cumulative interest, rate impact scenarios, term comparison

Cumulative interest paid each year on your $320,000 loan at 6.8%.

Year	Annual Interest	Cumulative Interest	% of Total Interest
1	$21,496	$21,496	5.0%
2	$21,258	$42,754	10.0%
3	$21,004	$63,758	14.9%
4	$20,733	$84,491	19.8%
5	$20,442	$104,933	24.6%
6	$20,131	$125,064	29.3%
7	$19,799	$144,863	33.9%
8	$19,443	$164,306	38.5%
9	$19,063	$183,369	42.9%
10	$18,656	$202,025	47.3%
11	$18,221	$220,246	51.6%
12	$17,755	$238,001	55.7%
13	$17,257	$255,258	59.8%
14	$16,725	$271,983	63.7%
15	$16,155	$288,138	67.5%
16	$15,546	$303,684	71.1%
17	$14,894	$318,578	74.6%
18	$14,197	$332,774	77.9%
19	$13,451	$346,226	81.0%
20	$12,654	$358,879	84.0%
21	$11,800	$370,680	86.8%
22	$10,888	$381,568	89.3%
23	$9,912	$391,480	91.6%
24	$8,868	$400,348	93.7%
25	$7,751	$408,099	95.5%
26	$6,557	$414,655	97.1%
27	$5,279	$419,935	98.3%
28	$3,912	$423,847	99.2%
29	$2,451	$426,298	99.8%
30	$887	$427,185	100.0%

First 5 years: you pay $104,933 in interest and only $19,598 in principal — that's why early extra payments make such a big difference.

Pro

Professional Interest Analysis

True total cost, inflation-adjusted interest, mortgage interest tax savings

Total cost of homeownership over the full 30-year loan term including taxes, insurance, and maintenance.

Annual Property Tax

Annual Home Insurance

Annual Maintenance

% of home value

True Total Cost Over 30 Years

$1,065,185

All mortgage payments + taxes + insurance + maintenance

Principal: $320,000

Interest: $427,185

Property Tax: $144,000

Insurance: $54,000

Maintenance: $120,000

Total Mortgage Paid

$747,185

P&I payments

Total Interest

$427,185

133% of principal

Total Taxes

$144,000

Over 30 years

Total Insurance

$54,000

Over 30 years

Total Maintenance

$120,000

1.0%% × 30 years

Cost Per Sq Ft Equivalent

$1,065,185

Full lifetime cost

How to Use the Mortgage Interest Calculator

This calculator focuses on the total interest cost of a mortgage — a number that often shocks first-time buyers. Enter your details to see exactly what interest will cost you over the life of the loan.

Quick Calculator

Enter your Home Price, Down Payment, Interest Rate, and Loan Term. The calculator instantly shows total interest paid, the interest-to-principal ratio, and the effective home cost (purchase price + all interest).

Advanced — Interest Deep Dive

Three analysis tabs show how interest accumulates year by year, how your total interest changes with rate adjustments of ±0.5% and ±1%, and a side-by-side comparison of all loan terms (10, 15, 20, 25, and 30 years) at your current rate.

Pro — Professional Analysis

The Pro tier adds three dimensions: True Cost Analysis includes property taxes, insurance, and maintenance over the full term so you can see the complete cost of homeownership. Inflation-Adjusted Cost shows what your interest payments are worth in today's purchasing power. Interest Tax Savings models the mortgage interest deduction against your standard deduction to see if itemizing actually benefits you.

The Formula

Monthly Payment (M) = P × [r(1+r)^n] / [(1+r)^n − 1]
Total Interest = M × n − P
Interest-to-Principal Ratio = Total Interest / Loan Amount
Effective Home Cost = Purchase Price + Total Interest
Real Interest = Nominal Interest / (1 + inflation rate)^years

Where P = loan principal, r = monthly interest rate (annual rate ÷ 12), and n = total number of monthly payments. Because interest is front-loaded, the majority of your early payments go to interest rather than reducing principal.

Worked Example: $400,000 Home

Sarah's 30-Year Mortgage Analysis

Sarah is buying a $400,000 home with 20% down ($80,000) at 6.75% for 30 years.

Loan Amount	$320,000
Monthly Payment (P&I)	$2,076
Total Payments Over 30 Years	$747,360
Total Interest Paid	$427,360
Interest-to-Principal Ratio	134%
Effective Home Cost	$827,360
Interest in First 5 Years	~$101,000
Interest in Last 5 Years	~$18,000

If Sarah chose a 15-year mortgage at 6.25% instead, her total interest drops to around $170,000 — saving over $257,000, though her monthly payment rises to about $2,743.

Frequently Asked Questions

Yes, on a 30-year mortgage at typical rates. At 6.75% for 30 years, you pay about 1.34× your loan amount in interest alone. On a 15-year mortgage at 6.25%, this drops to about 0.53×. The higher the rate and the longer the term, the more interest dominates the total cost.

Extra payments go directly to principal. A lower balance means less interest accrues each month. An extra $300/month on a $320,000 loan at 6.75% can save over $120,000 in total interest and pay off the loan about 8 years early. Use our Extra Payments Calculator for precise modeling.

As of 2024, you can deduct interest on up to $750,000 of mortgage debt ($375,000 if married filing separately). Interest on the portion above that limit is not deductible. This limit applies to loans originated after December 15, 2017. Older loans may have a $1 million cap under prior law.

Yes in isolation — but watch for tradeoffs. Buying points to get a lower rate costs money upfront. An ARM may start lower but can reset higher. Refinancing to a lower rate resets your amortization clock. Always compare total interest paid including any fees and points, not just the monthly payment.

Fixed mortgage payments stay the same in nominal terms but decrease in real (inflation-adjusted) terms. At 2.5% annual inflation, a $2,000 payment in year 30 costs the equivalent of about $960 in today's dollars. This is why financial advisors sometimes say a fixed mortgage is an inflation hedge — you're repaying in increasingly cheaper dollars.