40-Year Mortgage Calculator
Compare 40-year mortgage payments against 15, 20, and 30-year terms. See exactly how much you save monthly vs how much extra you pay in total interest — and whether the math actually works in your favor.
| Term | Rate | Monthly Payment | Total Interest | vs 30-Year |
|---|---|---|---|---|
| 15-Year | 6.500% | $3,484 | $227,197 | +$823/mo |
| 20-Year | 6.750% | $3,041 | $329,949 | +$380/mo |
| 30-Year (standard) | 7.000% | $2,661 | $558,036 | — |
| 40-Year (this calc) | 7.250% | $2,559 | $828,170 | -$103/mo |
The Monthly Savings vs Total Cost Tradeoff
| Term | Monthly | Yr 10 Balance | Total Interest | Total Cost |
|---|---|---|---|---|
| 15-Year | $3,484 | $178,085 | $227,197 | $627,197 |
| 20-Year | $3,041 | $264,880 | $329,949 | $729,949 |
| 30-Year | $2,661 | $343,250 | $558,036 | $958,036 |
| 40-Year | $2,559 | $375,077 | $828,170 | $1,228,170 |
Does Investing the Monthly Savings Beat the Extra Interest?
If you take the $103 saved monthly (40yr vs 30yr) and invest it at market returns, does it offset the higher total interest cost?
How to Use This 40-Year Mortgage Calculator
Compare a 40-year mortgage against 15, 20, and 30-year terms to understand the exact monthly savings and total cost tradeoff.
Quick Comparison
Enter your Loan Amount, 30-Year Rate (your base rate for a standard loan), and the 40-Year Rate (typically 0.25-0.50% higher). The calculator automatically assigns appropriate rates for 15 and 20-year terms and shows all four options side by side with monthly payments, total interest, and comparison vs the 30-year standard.
Advanced: Equity Buildup and Availability
The equity buildup table shows how much of your principal you have paid off at years 5, 10, 15, and 20. The 40-year is dramatically slower — a critical risk factor. The availability section explains where to find 40-year mortgages, since they are not available through standard conforming channels.
Pro: Wealth Comparison and Risk Analysis
The wealth comparison calculates whether investing the monthly savings at market returns beats the extra interest cost — a key question for the "pay less now, invest the difference" strategy. The refinance strategy section shows the total cost of starting with a 40-year and refinancing to 30-year in years 3, 5, 7, or 10.
How 40-Year Mortgage Payments Are Calculated
Where:
P = Loan principal
r = Monthly interest rate (annual rate ÷ 12)
n = Total number of payments (years × 12)
40-Year: n = 480 payments
30-Year: n = 360 payments
Example at $400,000 at 7.25%:
40-Year monthly: $2,591
30-Year monthly at 7.0%: $2,661
Monthly savings: $70
Extra total interest: ~$134,000 over the full term
Example: $400,000 Loan Across All Terms
James is buying in a high-cost market and weighing his options
| Term | Rate | Monthly | Total Interest | vs 30-Year |
| 15-Year | 6.50% | $3,484 | $227,000 | +$823/mo, saves $343K |
| 20-Year | 6.75% | $3,037 | $328,800 | +$376/mo, saves $241K |
| 30-Year | 7.00% | $2,661 | $558,000 | Baseline |
| 40-Year | 7.25% | $2,591 | $683,000 | -$70/mo, costs $125K more |
The 40-year saves only $70/month vs 30-year but costs $125,000 more in total interest. The 15-year saves $331,000 in interest but requires $823 more per month. James chose the 30-year for the balance of manageable payments and reasonable total cost.