Free Mortgage Calculator: Monthly Payment, Total Interest, Early Payoff
Calculate your monthly mortgage payment and total interest with the standard fixed-rate amortization formula. Run extra-payment scenarios to see how many years and dollars you save. 100% client-side — loan figures never leave your browser.
Standard Amortization Formula
Real fixed-rate mortgage math (M = P·r·(1+r)ⁿ / ((1+r)ⁿ−1)) — not a back-of-envelope approximation. Handles zero-interest edge case correctly.
Extra-Payment Scenarios
Add an optional extra monthly principal payment. We re-amortize month-by-month and tell you exactly how many years AND dollars in interest you save.
Year-by-Year Summary
See principal paid, interest paid, and ending balance for every year of the loan — perfect for spotting when the equity scale tips from interest-heavy to principal-heavy.
100% Client-Side
Loan amount, interest rate, and your full amortization schedule stay entirely in your browser. No upload, no save, no analytics.
What this mortgage calculator computes
This free mortgage calculator finds your monthly principal-and-interest payment from three inputs: loan amount, annual interest rate, and term in years. It uses the standard fixed-rate amortization formula the CFPB says lenders use, then runs a month-by-month simulation to show total interest, total paid, a year-by-year balance, and how many years and dollars an extra monthly payment saves. It runs 100% in your browser — loan figures never leave your device.
The result is your P&I only — the loan-specific number you can compare cleanly across lenders. Your full housing cost is PITI (principal, interest, taxes, insurance); add monthly property tax and homeowner's insurance to the figure here for a complete estimate. For other money math, use the loan calculator for auto and personal loans, the compound interest calculator for savings growth, and the percentage calculator for rate and down-payment math.
The amortization formula this tool uses
The monthly principal-and-interest payment for a fixed-rate mortgage is:
P · r · (1 + r)ⁿ
M = ─────────────────────
(1 + r)ⁿ − 1M = P·[r(1+r)^n] / [(1+r)^n − 1]
- M — the monthly principal-and-interest payment (the number you solve for)
- P — principal: the loan amount you borrow
- r — the monthly interest rate as a decimal: the annual rate ÷ 12 (so 6.5% becomes 0.065 ÷ 12 = 0.00541667)
- n — the total number of monthly payments: the term in years × 12 (so 30 years = 360)
This matches the standard formula the Consumer Financial Protection Bureau (CFPB) describes for amortizing loans, and the same math Freddie Mac and every fixed-rate lender uses. The zero-interest special case degenerates to M = P / n; this tool handles that branch explicitly so a 0% simulation never divides by zero.
Worked example: $300,000 at 6.5% for 30 years
Enter P = $300,000, rate = 6.5%, and term = 30 years. Here is the math, step by step, matching exactly what the calculator above returns.
- Monthly rate:
r = 0.065 ÷ 12 = 0.00541667 - Number of payments:
n = 30 × 12 = 360 - Growth factor:
(1 + r)^n = 1.00541667^360 = 6.99179797 - Numerator:
P · r · (1+r)^n = 300000 × 0.00541667 × 6.99179797 = 11,361.67 - Denominator:
(1+r)^n − 1 = 6.99179797 − 1 = 5.99179797 - Monthly payment:
M = 11,361.67 ÷ 5.99179797 = $1,896.20
Over 360 payments that is $682,633.47 total paid, of which $382,633.47 is interest — more than the home itself. In month one, interest is $300,000 × 0.00541667 = $1,625.00 and only $271.20 reduces principal. That ratio inverts over the life of the loan, which is why the year-by-year schedule in the tool above is worth reading.
US 30-Year Fixed Mortgage Rates: Historical Context
| Decade | Average Rate | Context |
|---|---|---|
| 1971–1980 | 8.9% | 1970s stagflation |
| 1981–1990 | 12.7% | Volcker rate-hike era; peaked at 18.4% in Oct 1981 |
| 1991–2000 | 7.9% | Greenspan post-recession easing |
| 2001–2010 | 6.0% | Housing boom + Great Recession trough |
| 2011–2020 | 4.0% | Post-GFC ultra-low rates |
| 2021–2025 | 5.9% | Inflation-driven Fed tightening |
Source: Freddie Mac Primary Mortgage Market Survey. Decade averages calculated from annual averages. Today's rate may be lower or higher than recent history; always get a written rate quote.
Why Extra Payments Are Mathematically Magical
The compounding mechanism that grows your debt at the bank also works in reverse when you pay it down faster. Three principles to internalise:
1. Early Payments Hit Hardest
An extra $100 in month 1 of a 30-year mortgage saves about $440 in interest over the life of the loan. The same $100 in month 300 saves about $10. Front-loaded extra payments are 40× more powerful than late ones.
2. Even Small Amounts Compound
$50 extra per month on a $300,000 / 6.5% / 30-year mortgage saves about $40,000 in interest and ~3 years — from a 0.6% increase in the monthly payment.
3. One Extra Payment Per Year
Sending a 13th payment each year (equivalent to one extra month divided across 12) typically shaves 4–5 years off a 30-year mortgage. Annual tax refund or bonus is a natural source.
4. Beware Prepayment Penalties
Some loans (rare in the US since 2014 Dodd-Frank rules; more common abroad) charge a fee for early payoff. Always confirm before accelerating — ask for the loan's prepayment clause in writing.
What this number excludes: the gap between P&I and PITI
The amortization formula only governs principal and interest (P&I). Your real monthly housing payment is PITI — P&I plus property Taxes and homeowner's Insurance, usually collected into an escrow account by the lender. This calculator deliberately shows P&I alone so the figure is lender-comparable, but it can understate your true outlay by hundreds of dollars a month.
Three costs the formula here does not include, and that you must add yourself:
- Property tax: roughly 0.3% of home value per year in Hawaii to 2.2%+ in New Jersey — on a $300,000 home that ranges from about $75 to $550 per month.
- Homeowner's insurance: commonly $100–$250/month, far higher in wildfire, flood, or hurricane zones.
- PMI (private mortgage insurance): typically 0.5%–1.5% of the loan per year when your down payment is under 20% — about $125–$375/month on a $300,000 loan, until you reach 20% equity. HOA dues, if any, are on top of all of this.
Bottom line: take the monthly payment from the tool above, then add your annual tax + insurance (+ PMI, + HOA) divided by 12 to estimate full PITI.
When NOT to Pay Extra on Your Mortgage
1. No Emergency Fund Yet
Pay yourself first. A 3–6 month emergency fund stops a job loss or medical bill from forcing a foreclosure. Liquidity beats equity in a crisis.
2. Higher-Interest Debt
Credit card at 22% or a personal loan at 12% should be paid before a mortgage at 6%. Always attack the highest rate first.
3. Employer 401(k) Match
A 50% or 100% employer match on retirement contributions is an immediate 50–100% return. Capture that before paying mortgage extra.
4. Low-Rate Mortgages
If you locked a 3% mortgage in 2021, the math favours putting extra money in index funds (long-term ~7% real return) over paying down the 3% debt.
Frequently asked questions
How is a monthly mortgage payment calculated?
The fixed-rate payment uses the amortization formula M = P·r·(1+r)^n / ((1+r)^n − 1), where P is the principal, r is the monthly rate (annual rate ÷ 12 as a decimal), and n is the number of monthly payments (years × 12). The payment stays constant; early on it is mostly interest, later mostly principal. This tool uses that exact formula, with M = P / n for the 0% edge case.
Does this calculator include property tax and insurance?
No. It computes principal and interest (P&I) only — the loan-specific number you can compare across lenders. Full housing cost is PITI: add your annual property tax and homeowner's insurance (plus PMI and HOA, if any) divided by 12 to the figure here for a complete monthly estimate.
How much can I save by paying extra each month?
More than most people expect. On a $300,000 loan at 6.5% for 30 years, an extra $100/month saves roughly $60,000 in interest and about 4 years; $200/month saves about $100,000 and 7 years. Extra payments attack high-balance early months where interest is heaviest. Enter an extra amount above to see your exact result.
What is the difference between a 15-year and 30-year mortgage?
Shorter term, higher payment, far less interest. On $300,000 at 6%: a 30-year is about $1,799/month with roughly $347,500 interest; a 15-year is about $2,532/month with roughly $155,700 interest — about $191,000 saved for $733 more per month. Many buyers take a 30-year and pay it like a 15-year for flexibility.
What is the difference between APR and the interest rate?
The interest rate drives the amortization formula and your P&I payment. APR is a regulatory disclosure that folds lender fees (origination, points, mortgage insurance) into one annualized number for comparison, so it is always at or above the rate when fees exist. Enter the interest rate here; use APR to compare quotes.
Can I use this for adjustable-rate mortgages (ARMs)?
Only for the initial fixed period. During the fixed years of a 5/1 ARM, the math equals a fixed-rate loan and this tool is accurate. After that the rate adjusts on an index plus margin, which no tool can predict. Run the numbers at both the initial rate and the contract's maximum rate; if the worst case is unaffordable, skip it.
Is my loan data sent to any server?
No. The formula, schedule, and extra-payment comparison all run in your browser in JavaScript. Loan amount, rate, term, and your full schedule never leave your device. There are no network requests and no analytics tied to your financial figures.
Estimates only — not financial advice
This calculator is for general educational use. Figures are estimates that exclude taxes, insurance, PMI, HOA dues, and lender fees, and they assume a fixed rate held for the full term. They are not financial advice. For exact numbers and a binding rate, consult a licensed mortgage professional or your lender, and review the official Loan Estimate document before signing anything.
Authoritative source: Consumer Financial Protection Bureau — How do mortgage lenders calculate monthly payments?
Last reviewed: June 2, 2026
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Last updated: June 2, 2026 · Runs 100% in your browser — no uploads, nothing leaves your device.
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