Mortgage Payment Calculator

Compare multiple mortgage scenarios side by side — 15 vs. 30 year terms, different interest rates, and varying down payments — to find the loan structure with the lowest total lifetime cost for your specific situation.

Why Comparing Loan Scenarios Changes Your Decision

The 15-year vs. 30-year decision involves more than just the payment difference: On a $400,000 loan, a 30-year mortgage at 7.0% costs $2,661/month in P&I while a 15-year at 6.5% costs $3,487/month — a difference of $826/month. But the 30-year costs $557,960 in total interest vs. $227,660 for the 15-year — a $330,300 lifetime difference. The monthly budget comparison tells only half the story; the scenario comparison quantifies the true cost of the extra monthly flexibility a 30-year provides.
Each 1% rise in interest rate costs approximately $58–$67 per month per $100,000 borrowed: On a $300,000 30-year loan, moving from 6.5% to 7.5% raises your P&I from $1,896 to $2,097 — $201 more per month and $72,360 more in total interest over 30 years. On a $500,000 loan the same 1% increase costs $335/month more ($120,600 over 30 years). Rate sensitivity analysis before committing to a loan — or before deciding whether to pay points — requires running these scenarios with real numbers rather than estimating the impact in your head.
Paying discount points to reduce your rate has a quantifiable break-even that depends entirely on your specific loan: One discount point costs 1% of the loan amount and typically reduces the rate by 0.25%. On a $450,000 loan, 2 points costs $9,000 and drops the rate from 7.25% to 6.75%, reducing the monthly P&I from $3,073 to $2,922 — saving $151/month. Break-even: $9,000 ÷ $151 = 59.6 months (just under 5 years). If you plan to stay more than 5 years, paying points is profitable; the scenario calculator runs this math instantly for any loan size and rate reduction.
The true comparison between loan options is total out-of-pocket cost, not just monthly payment: Total out-of-pocket equals your down payment plus all monthly payments for the full term — this is the money that leaves your household across the life of the loan. A 30-year mortgage on a $380,000 loan at 7% costs $2,531/month P&I — over 360 payments that's $911,160 plus $76,000 down payment = $987,160 total out-of-pocket. A 15-year at 6.5% costs $3,317/month — over 180 payments that's $597,060 plus the same $76,000 = $673,060 total. The 15-year option costs $314,100 less in total dollars spent, despite having the higher monthly payment.
Down payment size affects both the monthly payment and the rate you qualify for: Increasing your down payment from 10% to 20% on a $420,000 home does two things: it reduces the loan from $378,000 to $336,000 (lowering the payment) and eliminates PMI ($220–$472/month). On top of that, a 20% down payment often qualifies you for a better interest rate — potentially 0.25%–0.5% lower — further reducing the payment. The scenario calculator reveals the compounded impact of all three effects simultaneously.

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How to Compare Mortgage Scenarios Effectively

Establish your baseline scenario first: Enter the most likely scenario — the home price you are targeting, the down payment you have available, and the rate your lender quoted. Note the monthly P&I payment and total interest. This becomes your reference point against which all other scenarios are measured.
Run the 15-year version of the same loan: Keep the same loan amount and enter a 15-year term with the rate your lender quoted for that term (typically 0.5%–0.75% lower than the 30-year rate). Compare the monthly P&I difference and the total interest savings. Determine whether your monthly budget can absorb the higher payment — and whether the lifetime savings justify the tighter cash flow.
Model the rate sensitivity range: Enter the same loan at your quoted rate minus 0.5%, at your quoted rate, and at your quoted rate plus 0.5%. This shows you the dollar-per-month range you are exposed to depending on whether rates move before you lock. If the difference between the low and high scenarios is $200/month, you know the cost of waiting vs. locking now.
Calculate the points break-even for your specific loan: Enter the loan at the current rate (no points) and again at the reduced rate with the points cost subtracted from your available cash (effectively increasing your loan amount by the point cost, or reducing your cash reserves by the point amount). Compare total interest paid under both scenarios and divide the point cost by the monthly savings to find the break-even month.
Determine total lifetime cost for each scenario: For each scenario, add the down payment to the total of all monthly payments over the full term. Rank the scenarios by total out-of-pocket cost rather than by monthly payment alone. The scenario with the lowest total lifetime cost is almost always the financially optimal choice, provided the monthly payment is within your budget.

Real-World Use Case

Robert and Tanya are deciding between four loan structures on a $465,000 home with $93,000 saved (20% down, $372,000 loan amount). They run all four scenarios through the calculator: Scenario A — 30-year at 7.125%: $2,506/month P&I, $529,160 total interest. Scenario B — 30-year at 6.875% (with 2 points costing $7,440): $2,442/month P&I, $507,960 total interest — break-even on the points at month 115 (9.6 years). Scenario C — 20-year at 6.75%: $2,874/month P&I, $317,760 total interest. Scenario D — 15-year at 6.5%: $3,242/month P&I, $211,560 total interest. Scenario D saves $317,600 vs. Scenario A and $296,400 vs. Scenario B — but requires $736/month more than Scenario A. They determine their budget can sustain Scenario C's $368/month premium over Scenario A, so they choose the 20-year term — cutting their interest by $211,400 while keeping the payment $368 below the 15-year option. Without the side-by-side comparison, they would have defaulted to the 30-year loan.

Best Practices for Mortgage Scenario Comparison

Always compare scenarios at the same loan amount and down payment: Lender quotes sometimes use different assumed down payments or roll closing costs into the loan differently, making the monthly payment appear lower. Before running a comparison, normalize all scenarios to identical loan amounts — comparing a $380,000 loan at 7% against a $395,000 loan at 6.75% (where closing costs were financed) understates the true cost of the higher-rate option.
Use total interest as the primary metric, not monthly payment: Selecting the loan with the lowest monthly payment is a common but costly heuristic. The 30-year term always wins on monthly payment, but it can cost $200,000–$400,000 more in total interest over the loan's life than a 15-year term. The correct optimization target is the loan with the lowest total interest that fits within your monthly budget — use the calculator to find that threshold.
Model the rate lock decision with a specific dollar cost: If you are considering whether to lock your rate now or float for 30 more days hoping for a rate decrease, quantify the gamble. A 0.125% rate increase on a $400,000 loan costs $31/month and $11,160 over 30 years. A 0.25% increase costs $62/month and $22,320 over 30 years. Knowing these numbers converts an anxiety-inducing decision into a straightforward risk-reward calculation.
Include the opportunity cost of a larger down payment in your comparison: Putting $30,000 additional down reduces a $400,000 loan to $370,000 — saving approximately $200/month at 7% and $56,000 in total interest over 30 years. But $30,000 invested in a diversified index fund at a historical 7% average annual return compounds to approximately $228,000 over 30 years. The scenario calculator reveals the mortgage side of the equation; comparing that savings against the opportunity cost of the capital is essential for a complete financial decision.
Re-run your scenario comparison after every rate change before locking: Mortgage rates can change by 0.125%–0.375% within a single week. Every time rates shift materially, your scenario comparison changes — the break-even on points moves, the 15-year vs. 30-year lifetime cost difference shifts, and the total interest on your baseline scenario updates. Running the comparison with current rates at the time of your rate lock decision ensures you are optimizing against real data, not the figures from your pre-approval three months earlier.

Performance & Limits

Multi-scenario parallel comparison: Enter up to three loan scenarios simultaneously with different rates, terms, or loan amounts — the calculator displays monthly payment, total interest, and total lifetime cost for all scenarios in a single side-by-side view for direct comparison.
Discount points break-even calculator: Input the points cost and rate reduction to instantly calculate the monthly savings, total interest savings over the loan term, and the exact break-even month — the point after which paying for points becomes financially beneficial.
Rate sensitivity table: Generate a table showing monthly payment and total interest across a range of interest rates (e.g., 6.0% through 8.0% in 0.25% increments) for a fixed loan amount and term — quantifying your exposure to rate movement before your rate lock decision.
15-year vs. 30-year direct comparison: Dedicated comparison mode that takes a single loan amount and runs both the 15-year and 30-year scenarios simultaneously at the appropriate rates, calculating the monthly payment differential, total interest differential, and the break-even month where the 15-year's higher payments are fully recovered through interest savings.
Total out-of-pocket lifetime cost: For each scenario, computes and displays the sum of down payment plus all monthly payments for the full term — the definitive total cost figure that accounts for both the upfront cash commitment and the full duration of monthly obligations.

Common Mistakes to Avoid

Choosing the 30-year term by default without running the 15-year comparison: Many borrowers automatically select the 30-year term for the lower payment without calculating whether they could afford the 15-year. The 15-year rate is typically 0.5%–0.75% lower than the 30-year, partially offsetting the higher payment from the shorter term. On a $320,000 loan, the monthly payment difference between a 30-year at 7.0% and a 15-year at 6.4% is approximately $600/month — but the interest savings over the loan life exceed $250,000. Failing to run this comparison because the 30-year "feels safer" costs hundreds of thousands of dollars over time.
Evaluating points purely on the monthly payment reduction without calculating break-even: A lender may present paying points as a straightforward monthly savings without mentioning the upfront cost or the break-even timeline. Two points on a $400,000 loan costs $8,000 upfront. If the monthly savings is $100, the break-even is 80 months (6.7 years) — meaning you need to stay in the home for nearly 7 years for the points to pay off. For a buyer who moves every 5–6 years on average, paying points is a net loss regardless of how attractive the lower rate looks.
Comparing a 30-year and 15-year loan at the same interest rate: Lenders offer lower interest rates on 15-year mortgages because the shorter repayment period represents lower default risk over a shorter lending horizon. Comparing a 15-year at the same rate as the 30-year overstates the monthly payment burden of the 15-year and understates the interest savings. Always use the actual quoted rate for each specific term when running the comparison.
Ignoring the investment return alternative when deciding between large and small down payments: A scenario comparison that shows $75/month in mortgage savings from a larger down payment looks compelling — but if that extra $25,000 down payment could earn 8% annually in a broad market index fund, it generates $2,000/year in the first year and compounds dramatically over the loan's life. The mortgage calculator shows the cost of borrowing; you must separately model what the capital could earn elsewhere to make a fully informed down payment decision.

Privacy & Security

All scenario calculations run locally in your browser: Every loan amount, rate, term, and comparison scenario you model executes in browser-side JavaScript — no financial data is sent to any server or third party at any point.
No scenario history tracked or stored: The mortgage scenarios you model are not saved, logged, or used to build a profile — each calculator session is independent and leaves no trace after the browser tab is closed.
No mortgage leads generated from your inputs: Your loan amounts, rates, and comparisons are not forwarded to lenders, brokers, or lead generation companies — this tool exists solely to help you perform your own independent analysis.
Session data cleared on navigation: All inputs, scenarios, and comparison results are cleared automatically when you navigate away from the calculator — no data persists between sessions in cookies, localStorage, or any other browser storage mechanism.

Frequently Asked Questions

How much more does a 30-year mortgage cost in total interest compared to a 15-year?

The total interest difference between a 30-year and 15-year mortgage is substantial and grows with the loan amount. On a $350,000 loan: at 7.0% for 30 years, you pay $488,440 in total interest; at 6.4% for 15 years (using the typical rate discount), you pay $190,080 in total interest — a difference of $298,360. On a $500,000 loan, that same comparison yields $697,760 in 30-year interest vs. $271,540 in 15-year interest — a $426,220 gap. The 15-year mortgage also typically carries a lower rate, which amplifies the savings beyond just the term reduction. For borrowers whose budget can support the higher monthly payment, the 15-year option is one of the most powerful wealth-building financial choices available in conventional lending.

Is it worth paying mortgage discount points to get a lower interest rate?

Whether points are worth paying depends entirely on your break-even timeline relative to how long you plan to keep the loan. The calculation: divide the points cost by the monthly payment savings to find the break-even month. Example: 1.5 points on a $425,000 loan costs $6,375 and reduces the rate from 7.125% to 6.75%, saving $105/month in P&I. Break-even = $6,375 ÷ $105 = 60.7 months (5.1 years). If you are confident you will stay in the home without refinancing for more than 5 years, paying the points generates a positive return — effectively a 5.1-year payback period on a risk-free guaranteed return. If you may move or refinance within 4 years, the points generate a net loss. Points are most valuable for buyers in stable long-term housing situations and least valuable for buyers in transitional phases of life.

How does a 0.5% interest rate difference change my total mortgage cost?

A 0.5% rate difference has a larger impact than most borrowers expect. On a $375,000 30-year mortgage: at 6.75%, P&I is $2,432/month and total interest is $500,520; at 7.25%, P&I is $2,559/month and total interest is $545,240 — a difference of $127/month and $44,720 in total interest over 30 years. On a $550,000 loan the same 0.5% spread costs $186/month more ($66,960 over 30 years). This quantifies why borrowers with strong credit scores (which can qualify for lower rates) or those who can pay even one discount point (to reduce the rate by 0.25%) can save tens of thousands over the life of the loan. Rate negotiations and credit score improvements that yield even small rate reductions have outsized long-term financial impacts.

Should I choose the lowest monthly payment or the lowest total interest when comparing mortgage options?

Optimizing for lowest total interest is almost always the superior financial strategy — provided the associated monthly payment fits within your budget without causing financial stress. The lowest monthly payment option (typically the 30-year loan) maximizes the total interest paid to the lender and minimizes equity building speed. The lowest total interest option (typically the 15-year or 20-year loan) requires a higher monthly commitment but results in dramatically less total money leaving your household. A practical middle ground: choose the longest term you need to keep the monthly payment comfortable, then make extra principal payments to capture some of the interest savings a shorter term would provide — without being locked into the higher required payment. The scenario calculator lets you model exactly where this optimum sits for your specific loan amount and budget.