Mortgage Interest Calculator 2026
Calculate exactly how much interest you'll pay on your mortgage over its full term. See your month-by-month amortization breakdown, estimate your mortgage interest tax deduction, and discover how extra payments could save you tens of thousands of dollars.
Mortgage Interest Calculator
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Your Results
Instant calculation
Total Interest
$357,124.57
Over loan lifetime
Monthly Payment
$1,769.79
Total Paid
$637,124.57
Interest % of Loan
127.5%
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How Our Mortgage Interest Calculator Works
Our mortgage interest calculator uses the standard amortization formula to instantly compute every aspect of your loan's interest cost. Enter your loan amount, interest rate, loan term, and optional extra monthly payment, then the tool outputs:
- Total interest paid over the full loan term
- Your fixed monthly principal-and-interest payment
- A complete month-by-month amortization schedule
- Total amount paid (principal + all interest)
- Estimated mortgage interest tax deduction (if you itemize)
- Interest savings from extra monthly payments
- Breakeven payoff date for extra payments
Step-by-Step Instructions
- 1
Enter your loan amount
The original principal you borrow — not the home price. Example: $400,000.
- 2
Enter your annual interest rate
Use the interest rate from your loan offer, not the APR. Example: 6.75%.
- 3
Select your loan term
30-year, 20-year, 15-year, or 10-year fixed are the most common in the U.S.
- 4
(Optional) Add extra monthly payment
Enter any amount you plan to pay above the required monthly payment to see interest savings.
- 5
Click Calculate
Instantly see your total interest, monthly payment, full amortization table, and tax deduction estimate.
Mortgage Interest Formula Explained
Understanding the math behind your mortgage helps you make smarter financial decisions. Here are the two key formulas our mortgage interest calculator uses.
// Monthly Payment (M)
M = P × [r(1 + r)ⁿ] / [(1 + r)ⁿ - 1]
// Where:
P = Principal loan amount
r = Monthly interest rate (Annual Rate ÷ 12)
n = Total number of payments (Years × 12)
// Monthly Interest Charge (I)
I = Remaining Balance × (Annual Rate ÷ 12)
// Real Example — Month 1:
$400,000 × (0.0675 ÷ 12) = $400,000 × 0.005625 = $2,250 interest
Total monthly payment = $2,594
Principal paid Month 1 = $2,594 - $2,250 = $344
New balance = $400,000 - $344 = $399,656
Total Interest Formula: Total Interest = (Monthly Payment × Total Payments) − Principal. For the example above: ($2,594 × 360) − $400,000 = $533,840. That means you pay more in interest than the original loan amount on a standard 30-year mortgage.
How Your Payment Splits Between Interest and Principal
In the early years of your mortgage, the vast majority of each payment covers interest because your outstanding balance is at its highest. This is called amortization. As you reduce the principal over time, the interest portion of each payment shrinks and more goes toward building equity.
| Loan Year | Interest Portion | Principal Portion | Interest Split |
|---|---|---|---|
| Year 1 | ~80% | ~20% | |
| Year 5 | ~74% | ~26% | |
| Year 10 | ~65% | ~35% | |
| Year 15 | ~52% | ~48% | |
| Year 20 | ~40% | ~60% | |
| Year 25 | ~24% | ~76% | |
| Year 30 | ~8% | ~92% |
Based on a $400,000 30-year mortgage at 6.75%. Percentages are approximate.
This is why financial experts consistently recommend making extra mortgage payments early in the loan — every extra dollar applied to principal in year 1 eliminates multiple dollars of future interest.
Mortgage Interest Tax Deduction 2026
One of the most important benefits of homeownership is the potential to deduct mortgage interest from your federal taxable income. Our mortgage interest deduction calculator estimates your deduction based on the 2026 IRS rules.
Who Can Deduct
- •You itemize deductions on Schedule A
- •Mortgage debt ≤ $750,000 (loans after Dec 15, 2017)
- •Mortgage debt ≤ $1,000,000 (loans before Dec 16, 2017)
- •Loan secured by your primary or second home
2026 Standard Deduction (Threshold)
- •Single filers: $16,100
- •Married Filing Jointly: $32,200
- •Head of Household: $24,150
- •Itemizing only helps if your total deductions exceed these amounts
How to Calculate Your Mortgage Interest Tax Deduction
Follow these four steps to estimate your annual tax savings from the home mortgage interest deduction:
- 1Locate your IRS Form 1098 from your mortgage servicer — it lists all mortgage interest paid during the year.
- 2Verify your outstanding mortgage balance doesn't exceed the $750,000 deduction limit.
- 3Add all other itemized deductions (state & local taxes within the 2026 federal SALT cap—generally $40,400 for most filers, with phase-downs at very high incomes—plus charitable contributions, etc.).
- 4If total itemized deductions exceed the standard deduction, the interest is deductible. Multiply the deductible interest by your marginal tax rate to estimate your tax savings.
📊 Real-World Example
* This is an estimate for illustrative purposes. Consult a tax professional for personalized advice. See IRS Publication 936 for complete rules on the home mortgage interest deduction.
Interest-Only Mortgage Calculator: How It Works
An interest-only mortgage calculator computes the reduced payment you owe during the interest-only period of your loan. During this phase — typically 5 to 10 years — your payment covers only the interest charge and your balance does not decrease.
// Interest-Only Monthly Payment
Payment = Loan Balance × (Annual Rate ÷ 12)
Example: $400,000 × (6.75% ÷ 12)
= $400,000 × 0.005625 = $2,250/month
vs. Full P&I payment at same rate: $2,594/month
The Risk of Interest-Only Loans
When the interest-only period ends, your loan converts to a fully amortizing loan for the remaining term. Because no principal was paid down, the new payment can jump dramatically. On the example above, after a 10-year interest-only period at 6.75%, the new payment for the remaining 20 years becomes approximately $3,041/month — a 35% increase overnight.
Interest-only mortgages can work well for investors with variable income or those who plan to sell before the adjustment date. For most primary-home buyers, a standard principal-and-interest mortgage is the safer long-term choice. Use our interest-only mortgage calculator to compare both payment types side by side.
How Extra Payments Reduce Total Mortgage Interest
Every extra dollar you pay toward your mortgage principal directly reduces your outstanding balance. A lower balance means less interest accrues each month, which means more of every future payment goes toward principal — a powerful compounding benefit.
Extra Payment Impact — $400,000 Loan at 6.75% (30-Year)
| Extra/Month | Interest Saved | Years Saved | Payoff |
|---|---|---|---|
| $0 (baseline) | — | — | 30 yrs |
| $100/month | ~$41,000 | ~2.5 yrs | 27.5 yrs |
| $250/month | ~$100,000 | ~5.5 yrs | 24.5 yrs |
| $500/month | ~$170,000 | ~9 yrs | 21 yrs |
| $1,000/month | ~$252,000 | ~14 yrs | 16 yrs |
Pro Tip: Bi-Weekly Payment Strategy
Instead of one monthly payment, split your payment in half and pay every two weeks. Because there are 52 weeks in a year, you end up making 26 half-payments — equivalent to 13 full monthly payments instead of 12. This one extra payment per year can shave 4–5 years off a 30-year mortgage with zero change to your monthly budget feel. Use our mortgage calculator to model the exact impact for your loan.
15-Year vs. 20-Year vs. 30-Year Mortgage: Interest Comparison
Loan term is the single biggest lever for controlling total mortgage interest. Choosing a shorter term costs more each month but saves an enormous amount over the life of the loan. Here's a side-by-side comparison for a $400,000 mortgage using representative 2026 rates.
30-Year at 6.75%
StandardMonthly Payment
$2,594
Total Interest
$534,000
Total Paid
$934,000
20-Year at 6.25%
Good BalanceMonthly Payment
$2,982
Total Interest
$316,000
Total Paid
$716,000
vs. 30-Year Savings
~$218,000
15-Year at 5.90%
Best SavingsMonthly Payment
$3,356
Total Interest
$204,000
Total Paid
$604,000
vs. 30-Year Savings
~$330,000
The 15-year mortgage saves over $330,000 in interest compared to a 30-year loan — more than the initial down payment on most homes. If you can handle the higher monthly payment, a shorter term is one of the best financial moves available to a homeowner. Use our refinance calculator to see whether refinancing from a 30-year to a 15-year makes sense today.
Factors That Determine Your Mortgage Interest Cost
Several variables control how much total interest you'll pay. Understanding each one lets you take action to reduce your borrowing cost before and during your loan.
Loan Amount
The principal is the foundation of your interest calculation. A $50,000 larger loan at 6.75% adds roughly $67,000 in total interest on a 30-year term. Maximize your down payment using our down payment calculator to borrow less.
Down Payment CalculatorInterest Rate
A 1% higher interest rate on a $400,000 30-year loan adds approximately $90,000 in total interest. Even 0.25% matters. Shop at least 3–5 lenders and compare APRs to secure the best rate.
Loan Term
The single largest variable after rate. A 15-year term saves $300,000+ in interest vs. a 30-year on a $400,000 loan. Even moving from 30 to 20 years saves roughly $218,000.
Credit Score
Borrowers with FICO scores above 760 typically qualify for rates 0.5%–1.0% lower than those with scores in the 620–659 range. Improving your credit score before applying can save tens of thousands.
Down Payment
A down payment of 20% or more eliminates PMI and typically qualifies you for a lower interest rate. Every extra dollar of down payment directly reduces your interest-bearing principal.
Calculate down paymentRefinancing
Refinancing when rates drop can dramatically reduce total interest. A drop from 7.5% to 6.5% on a $400,000 loan saves over $80,000 in remaining interest. Run the numbers first.
Refinance Calculator10 Proven Tips to Pay Less Mortgage Interest
Shop multiple lenders
Get at least 3–5 loan offers. Even a 0.25% rate difference saves ~$20,000 on a $400,000 30-year loan. Use Credible, LendingTree, or your local credit union.
Improve your credit score before applying
Pay down revolving debt to below 30% of your credit limit and dispute any errors on your credit report. Moving from a 680 to a 760 score can knock 0.5%–0.75% off your rate.
Make a 20% down payment
Eliminates PMI (usually $100–$200/month) and often qualifies you for a lower interest rate. Use our down payment calculator to set a savings target.
Choose a shorter loan term
A 15-year mortgage carries a lower rate and far less total interest. If the payment feels too high, consider a 20-year as a middle ground.
Make one extra payment per year
Apply a 13th payment each January. On a $400,000 30-year loan at 6.75%, this alone saves roughly $60,000 in interest and cuts 4 years off the loan.
Pay bi-weekly instead of monthly
Automatically makes 13 monthly-equivalent payments per year. Ask your servicer if they offer a formal bi-weekly program — or manually make an extra half-payment each month.
Round up your monthly payment
Rounding $2,594 to $2,600 adds $106/month to principal, saving roughly $27,000 and 2 years over the loan life.
Refinance when rates drop 0.75% or more
Compare your break-even point (closing costs ÷ monthly savings) to how long you plan to stay. Use our refinance calculator to check if refinancing makes sense today.
Apply windfalls to principal
Tax refunds, bonuses, or inheritances applied directly to mortgage principal create outsized long-term interest savings.
Consider mortgage points
Paying 1 discount point (1% of loan amount) typically lowers your rate by 0.25%. On a $400,000 loan, one point costs $4,000 and saves ~$22,000 in interest over 30 years.
How Is Interest Calculated on a HELOC vs. a Mortgage?
Both products use your home as collateral, but interest accrues very differently.
| Feature | Mortgage | HELOC |
|---|---|---|
| Interest type | Fixed or ARM | Variable (Prime + margin) |
| Calculation basis | Monthly on remaining balance | Daily on outstanding draw |
| Payment structure | Fixed P&I every month | Interest-only during draw period |
| Rate risk | Low (fixed) / Medium (ARM) | Higher — rate changes monthly |
| Tax deductibility | Up to $750K of acquisition debt | Only if used for home improvement |
| Best for | Home purchase / primary financing | Flexible access to home equity |
For HELOC interest calculations, visit our HELOC calculator.
Frequently Asked Questions About Mortgage Interest
Editorial Standards & Disclaimer
The calculations and content on this page are reviewed by our editorial team of licensed financial professionals and updated annually to reflect current IRS rules, federal mortgage guidelines, and market conditions. All figures are for illustrative purposes only.
This tool does not constitute financial, tax, or legal advice. Consult a qualified mortgage lender or HUD-approved housing counselor for advice tailored to your situation. For official tax guidance see IRS Publication 936. For mortgage rate data see the Freddie Mac Primary Mortgage Market Survey.