Part of our guide to How Much House Can You Actually Afford?
Most mortgage calculators return principal and interest and stop there. That figure is not what leaves your account each month, and the gap is large enough to change what you can afford.
Your full monthly payment — principal, interest, property tax, home insurance, HOA dues and PMI where it applies — plus the total interest over the life of the loan. Taxes and insurance are the parts buyers underestimate, and both continue rising after your principal and interest are fixed.
How the calculation works
The loan portion uses the standard amortised payment formula:
M = P · r / (1 − (1 + r)^−n)where P is the amount borrowed, r is the monthly rate (the annual rate divided by twelve), and n is the number of monthly payments. A 0% loan is handled separately, because that formula divides by zero — the payment is simply the principal divided by the term.
The remaining components are not part of the loan at all. Property tax and insurance are annual figures divided by twelve and collected into escrow alongside the payment. HOA dues are a flat monthly amount. PMI is applied only while the loan exceeds 80% of the purchase price, calculated as an annual rate against the loan balance and divided by twelve.
A worked example
A $400,000 home with $80,000 down, at 6.5% over 30 years, with $6,000 annual property tax and $1,800 annual insurance:
| Component | Monthly |
|---|---|
| Principal and interest | $2,023 |
| Property tax | $500 |
| Home insurance | $150 |
| PMI (loan is exactly 80% LTV) | $0 |
| Full payment | $2,673 |
Those two escrow items add $650 to every payment — $7,800 a year. A calculator showing only principal and interest would understate the monthly cost by that amount, which is enough to change what a household can carry.
Now drop the down payment to $20,000 and hold everything else constant:
| 20% down | 5% down | |
|---|---|---|
| Loan amount | $320,000 | $380,000 |
| Loan-to-value | 80% | 95% |
| Principal and interest | $2,023 | $2,402 |
| PMI | $0 | $158 |
| Full payment | $2,673 | $3,210 |
The smaller deposit costs $538 more every month, and $158 of that buys you nothing — PMI protects the lender, not you.
What the payment looks like at other loan sizes
Principal and interest only, 30-year term. Add your own property tax, insurance and any HOA on top — on a typical American property those add several hundred dollars a month, as the worked example above shows.
| Loan amount | 5.5% | 6% | 6.5% | 7% | 7.5% |
|---|---|---|---|---|---|
| $200,000 | $1,136 | $1,199 | $1,264 | $1,331 | $1,398 |
| $250,000 | $1,419 | $1,499 | $1,580 | $1,663 | $1,748 |
| $300,000 | $1,703 | $1,799 | $1,896 | $1,996 | $2,098 |
| $350,000 | $1,987 | $2,098 | $2,212 | $2,329 | $2,447 |
| $400,000 | $2,271 | $2,398 | $2,528 | $2,661 | $2,797 |
| $500,000 | $2,839 | $2,998 | $3,160 | $3,327 | $3,496 |
Read across a row and the cost of the rate becomes concrete. On a $300,000 loan, moving from 6% to 7% adds $197 a month — about $71,000 across thirty years, for the same house. That single row is the strongest argument there is for shopping more than one lender. We put numbers to that in what a 6.7% mortgage rate actually costs.
15 years against 30
Same $300,000 loan at 6.5%:
| 30-year | 15-year | |
|---|---|---|
| Monthly principal and interest | $1,896 | $2,613 |
| Total interest paid | $382,633 | $170,398 |
The shorter term costs $717 more a month and saves $212,235 in interest. Whether that trade is available to you is a budget question, not a maths question — and taking the 30-year and overpaying voluntarily gets you most of the benefit while keeping the lower payment as a fallback. The extra mortgage payment calculator works out how much.
Why your lender's number will differ
This calculator is not wrong when it disagrees with a lender quote — it is answering a narrower question. A lender's figure typically includes things this does not:
- Prepaid escrow at closing. Lenders usually collect several months of tax and insurance up front to seed the escrow account. It affects cash needed at closing, not the recurring payment.
- Mortgage insurance that behaves differently. FHA loans carry an upfront premium plus an annual one that, on most current FHA loans, lasts the life of the loan rather than falling away at 78% LTV. This calculator models conventional PMI.
- Discount points. Paying points buys a lower rate. The quoted rate may already assume you are buying them.
- A different tax estimate. Lenders often use the current owner's assessment, which can be reassessed after a sale.
If your figure and theirs differ by a few hundred dollars, escrow assumptions are almost always the reason.
How to read the result
The monthly total is what to budget against, not the principal and interest figure.
Taxes and insurance rise over time. Your principal and interest are fixed on a fixed-rate loan; the escrow portion is not. A payment that fits comfortably today can drift upward for reasons unconnected to your mortgage.
PMI is temporary on a conventional loan. It is removable at 80% loan-to-value on request and terminates automatically at 78%. On most FHA loans it behaves very differently — see how much down payment you actually need.
Total interest is worth looking at once. Over thirty years it is frequently comparable to the amount borrowed. Seeing it is the strongest argument for a shorter term or extra payments, if you can afford either.
What escrow actually is
Property tax and insurance are not part of the loan. Your lender collects roughly a twelfth of each annual bill alongside the mortgage payment, holds it in an escrow account, and pays the bills when they come due.
Two consequences follow, and both catch people out:
Your payment changes even on a fixed-rate mortgage. Principal and interest are fixed. Tax and insurance are not. When either bill rises, the lender recalculates the escrow portion — usually once a year — and your payment moves with it.
An escrow shortage arrives as a lump sum or a raised payment. If the bills came in higher than projected, the account runs short. Lenders typically offer to spread the shortfall over the next twelve months, which raises the payment twice over: once for the higher ongoing bill, once to refill the account.
Assumptions this makes
Stated plainly, because a number is only as good as what produced it:
- A fixed rate for the whole term. An adjustable-rate loan is a different calculation — see fixed vs adjustable rate mortgage.
- Conventional PMI at 0.5% annually unless you change it, applied only while the loan exceeds 80% of the purchase price. Real PMI rates vary with credit score and deposit size.
- Property tax and insurance stay flat. They will not. This is a snapshot of the opening payment, not a projection.
- No extra payments, no recast, no refinance.
- The result is principal, interest and escrow only. Maintenance, utilities and closing costs are excluded.
Important considerations
This estimates a payment. It does not tell you what you can afford, which is a different question with different inputs — see how much house can you actually afford.
Use the real property tax figure. It is public record for any specific address, and it varies enormously between jurisdictions. An estimate here is the single largest source of error in the result.
Get an actual insurance quote for the specific property rather than using a general figure.
The result excludes closing costs, maintenance, and utilities. Closing costs alone are a separate and substantial sum — see what closing costs actually pay for.
Related reading
- How much house can you actually afford?
- How much down payment do you actually need?
- Fixed vs adjustable rate mortgage
- What closing costs actually pay for
- Rent vs buy — the arithmetic behind the argument
This is an estimate for general information, not a loan offer or financial advice. Your lender's figures are the ones that count — see our disclaimer.
Frequently asked questions
Does this include taxes and insurance?
Yes. That is the point — principal and interest alone typically understate the real monthly cost substantially, because property tax and insurance are paid through the same monthly escrow.
What is PMI and why does it appear?
Private mortgage insurance, charged while the loan exceeds 80% of the home's value. It protects the lender, not you. The calculator shows it only when the loan-to-value is above 80%.
When does PMI stop?
On a conventional loan you may request cancellation at 80% loan-to-value, and the lender must terminate it automatically at 78%. So it is a temporary cost, not one for the full term.
Why is my lender's figure different?
Usually because of the tax and insurance estimates, which vary by property rather than by loan. Use the actual tax bill for the specific address — it is public record — instead of an average.
Does it account for extra payments?
Not yet. This calculates the scheduled payment. Extra payments reduce the term and total interest considerably, and that is a separate tool.
What is the monthly payment on a $300,000 mortgage?
At 6.5% over 30 years, principal and interest come to $1,896 a month. Property tax, home insurance and any HOA dues are added on top of that and are paid through escrow — on a typical property they add several hundred dollars more. The table above shows the figure at other loan sizes and rates.
How much does a 1% higher rate cost?
On a $300,000 loan over 30 years, moving from 6% to 7% raises the payment from $1,799 to $1,996 — about $197 a month, or roughly $71,000 in extra interest across the full term for exactly the same house.
Is a 15-year mortgage worth the higher payment?
On a $300,000 loan at 6.5% the 15-year term costs $717 more each month and saves $212,235 in interest. Whether that is affordable is a budget question. Taking the 30-year and overpaying voluntarily captures much of the same benefit while keeping the lower payment available if your income changes.
Why does my payment go up on a fixed-rate loan?
Because only principal and interest are fixed. Property tax and insurance are collected through escrow and recalculated when those bills change, so the total payment moves even though the loan rate never does.
Sources
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