Mortgage Payment Calculator

How mortgage payments are calculated

Your monthly mortgage payment is determined by four variables: the loan amount (purchase price minus down payment), the interest rate, the loan term, and any additional monthly costs you fold in (taxes, insurance, HOA). The core calculation uses the standard PMT formula from financial mathematics:

What this formula produces is your principal & interest (P&I) payment — the amount that actually goes toward paying off your loan. On top of this, most lenders collect property taxes and homeowner's insurance in escrow (added to your monthly payment and held until due), plus any HOA fees if applicable.

Understanding the split between principal and interest is important. In the early years of a 30-year mortgage, a surprisingly large share of your monthly payment is interest — not equity-building principal. On a $400,000 loan at 6.8% over 30 years, your first payment is roughly $2,617/month P&I, but about $2,267 of that (86%) goes to interest and only $350 reduces your balance. By year 20, the split flips. This is called amortisation — the mathematical consequence of charging interest on a declining balance.

The amortisation schedule in this calculator shows every payment across the full loan term. Expand it to see exactly how much of each payment goes to principal vs interest, and watch your equity build over time.

How down payment affects your monthly costs

Your down payment is the single biggest lever you control at purchase. A larger down payment reduces your loan amount, which reduces both your monthly P&I and the total interest you'll pay over the life of the loan. But its effects go further than arithmetic.

The 20% threshold and PMI: In the United States, conventional loans require private mortgage insurance (PMI) when the down payment is below 20% of the purchase price. PMI typically costs 0.5%–1.5% of the loan amount per year — on a $380,000 loan, that's $1,900–$5,700 annually, or $158–$475/month added to your payment. PMI does not build equity; it protects the lender. Once your loan-to-value (LTV) ratio reaches 80% through payments or appreciation, you can request cancellation. The 20% threshold is therefore not just a nice round number — it's the PMI cliff.

The opportunity cost argument: Putting 20% down on a $500,000 home means $100,000 in cash deployed into a single illiquid asset. If you could invest that $100,000 and earn 8–10% annually (historical S&P 500 average), versus paying 6.8% mortgage interest on a larger loan amount, the math may favor a smaller down payment. But this comparison is more nuanced than it looks: it ignores risk, liquidity, PMI cost, tax deductibility, and your personal comfort with debt. There is no universally correct answer.

Canadian norms: In Canada, the stress test rules require qualifying at the higher of your contract rate + 2% or the Bank of Canada's benchmark rate (~5.25% at time of writing). This effectively reduces purchasing power. Canadian buyers with less than 20% down must carry CMHC mortgage default insurance, which adds a premium of 2.8%–4% of the insured loan to the mortgage amount. Buyers putting 5% down on a $500,000 home pay a $19,000 insurance premium — typically folded into the mortgage, not paid upfront.

Fixed vs variable rates — what to model in 2026

As of 2026, most North American buyers choosing between fixed and variable rate mortgages are navigating an environment where fixed rates have come down from their 2023 peaks but remain elevated by historical standards. The choice involves both math and psychology.

Fixed rates give you certainty. Your payment stays identical for the entire term. You can budget precisely, and you're protected if rates rise. The cost of that certainty is typically a modest premium over the best variable rate available at the same time. For most first-time buyers and people with limited financial buffer, fixed is the right default — not because it always wins mathematically, but because it eliminates payment shock risk.

Variable rates are typically set at a spread over the central bank's policy rate (the Fed Funds Rate in the US, the Bank of Canada's overnight rate in Canada). They fluctuate as rates change. When rates fall, variable-rate borrowers benefit automatically. Historically, over long periods, variable rates have tended to cost slightly less than fixed — but this is not guaranteed, and the months when rates spike can be financially painful if you're stretched.

What to model: Use this calculator to run three scenarios. First, model your actual expected rate (the rate you've been quoted or expect to qualify for). Then model rate + 2% (a stress test scenario — what if rates rise?). Then model rate - 1% (if rates fall, what's the monthly saving and would it justify going variable?). The difference between these scenarios shows your personal rate sensitivity.

For Canadian buyers: If you're taking a variable rate mortgage, ensure you qualify under the stress test at the higher of contract rate + 2% or the BoC benchmark. Stress test your payment at the higher rate in this calculator to confirm you can service the debt under adverse conditions.

Prepayment strategies — how extra payments compound

One of the least-appreciated features of a fixed mortgage is that you are not locked into making only the minimum payment. Any extra dollars you apply to principal directly reduce the balance on which interest is charged — and the savings compound because every future interest charge is calculated on a lower balance.

Extra monthly payments: Adding even $200–$300/month to a 30-year mortgage at 6.8% can shave 3–5 years off the loan term and save $40,000–$80,000 in total interest, depending on the loan amount. Use the prepayment scenario section of this calculator to see the exact numbers for your situation. The key insight: the earlier in the loan you make extra payments, the larger the compounding benefit, because you're reducing the base that generates decades of future interest charges.

The "round up your payment" trick: One of the simplest prepayment strategies requires no discipline to maintain — round your payment up to the nearest hundred or thousand. On a $2,617 monthly payment, rounding to $2,700 adds $83/month with minimal lifestyle impact, but across 30 years at 6.8%, you'd save roughly $24,000 in interest and pay off approximately 14 months early. Small, automatic, painless.

Accelerated bi-weekly payments: Many lenders (particularly in Canada, where this is the norm) offer accelerated bi-weekly payments. Instead of 12 monthly payments, you make 26 half-payments. Mathematically, this equals 13 full monthly payments per year — one extra payment annually. On a $400,000 mortgage at 6.5% over 25 years, accelerated bi-weekly payments alone can save over $35,000 in interest and cut roughly 3 years from the amortisation.

Lump sum payments: If you receive a bonus, inheritance, or tax refund, a one-time lump sum applied to mortgage principal can be extremely effective. A $10,000 lump sum applied in year 1 of a $400,000/6.8%/30-year mortgage saves approximately $26,000 in future interest and shortens the term by about 13 months — because that $10,000 eliminates 13 months of future interest charges across 30 years.

Common mistakes first-time buyers make

The most expensive mistake first-time buyers make is calculating affordability using only the principal and interest payment — and then being caught off-guard by the real monthly cost once taxes, insurance, and HOA are added. Use the "Additional Costs" inputs in this calculator to model your true all-in monthly cost before you make an offer.

Forgetting about closing costs: Closing costs are typically 2%–5% of the purchase price in the US (3%–4% in Canada). On a $450,000 home, that's $9,000–$22,500 in cash needed at closing, on top of your down payment. These include lender origination fees, appraisal, title insurance, property transfer taxes (Canada), and pre-paid items like property taxes and insurance. Many buyers drain their savings for the down payment and then scramble to cover closing costs. Know this number before you make an offer.

Ignoring maintenance budgets: A common rule of thumb is to budget 1%–2% of your home's value annually for maintenance and repairs. On a $450,000 home, that's $4,500–$9,000/year — $375–$750/month that should factor into your affordability calculation. Older homes and climates with extreme weather may require more. Buyers who don't budget for maintenance often face financial strain the first time a major system (roof, HVAC, water heater) needs replacement.

Not comparing lenders: The rate difference between the first lender you talk to and the best rate available is typically 0.25%–0.75%. On a $400,000 loan over 30 years, 0.5% higher rate costs about $44,000 in extra interest. Shopping 3–5 lenders (including online lenders and credit unions, not just your bank) is one of the highest-ROI financial decisions you'll make. Mortgage rate shopping within a 45-day window counts as only one hard inquiry on your credit report.

Underestimating how fast the market moves: Getting pre-approved takes time. Buyers who start shopping before they're pre-approved often lose homes to pre-approved buyers who can close faster. Get pre-approved before you start making offers — and if you're in a competitive market, ask your lender about underwriting timelines and whether they offer "fully underwritten" pre-approvals, which carry more weight than basic pre-qualifications.

Frequently asked questions