I’ve spent 37 years in mortgage and commercial lending. In that time, I’ve watched plenty of homebuyers walk into my office confident in what they would pay each month and the cost to close, only to find out it’s going to be way more than what those mortgage calculators on the web told them it would be. That conversation is never easy. And it doesn’t have to happen.
So I decided to run a test. I took a straightforward purchase scenario, one that represents a typical first-time buyer in Texas, and put it through the five most prominent mortgage calculator websites returned by a Google search for “Mortgage Calculator.” I then compared each calculator’s output to two actual verified lender quotes I obtained for the same scenario.
The results are educational. And sobering.
The Test Scenario
Every calculator was given identical inputs. Here’s what we used.
Purchase Scenario: Texas
| Purchase Price | $400,000 |
| Down Payment | 5% ($20,000) |
| Loan Amount | $380,000 |
| Interest Rate | 6.000% |
| Origination Fee | 1% |
| Loan Term | 30 years, fixed |
| Property State | Texas (Tarrant County) |
| FICO Score | 660 (used for PMI rate) |
| HOA Dues | None |
| Hazard Insurance collected | 12 months prepaid + 2-month escrow reserve |
| Property Taxes collected | 3-month escrow reserve |
| Prepaid Interest | 30 days |
Two lender quotes for this specific scenario were obtained by the author (37 years in mortgage lending) and used as the accuracy benchmark. Calculator outputs for the five tested websites were recorded in August 2026 using the inputs above; results may differ at other dates or under different inputs. This comparison covers only the five calculators tested and does not characterize all mortgage calculators on the market.
Monthly Payment Comparison
How each calculator estimated the total monthly housing payment.
Q1, Q2 = Verified lender quotes • YMT = yourmortgagetoolbox.com • WC1-WC5 = Website Calculators 1-5 (top Google results)
| Payment Component | Verified Quote Q1 |
Verified Quote Q2 |
YMT | Website Calc 1 |
Website Calc 2 |
Website Calc 3 |
Website Calc 4 |
Website Calc 5 |
|---|---|---|---|---|---|---|---|---|
| Principal & Interest | $2,278 | $2,278 | $2,278 | $2,278 | $2,278 | $2,278 | $2,278 | $2,278 |
| Hazard Insurance | $300 | $233 | $394 | $125 | $125 | $66 | $79 | $213 |
| Property Taxes | $595 | $600 | $549 | $250 | $400 | $263 | $400 | $500 |
| PMI | $367 | $367 | $367 | $158 | $0 | $0 | $241 | $327 |
| Total Monthly Payment | $3,541 | $3,479 | $3,588 | $2,812 | $2,803 | $2,607 | $2,998 | $3,318 |
Cash to Close Comparison
The full amount a buyer must bring on purchase day, not just the down payment.
Q1, Q2 = Verified lender quotes • YMT = yourmortgagetoolbox.com • WC1-WC5 = Website Calculators 1-5
| Component | Verified Quote Q1 |
Verified Quote Q2 |
YMT | Website Calc 1 |
Website Calc 2 |
Website Calc 3 |
Website Calc 4 |
Website Calc 5 |
|---|---|---|---|---|---|---|---|---|
| Closing Costs | $9,014 | $8,514 | $7,356 | $0 | $0 | $0 | $0 | $0 |
| Prepaids (taxes, insurance, interest) |
$8,159 | $7,252 | $9,130 | $0 | $0 | $0 | $0 | $0 |
| Total Cash to Close | $37,173 | $35,766 | $36,486 | $20,000 | $20,000 | $20,000 | $20,000 | $20,000 |
Accuracy Summary
Percentage accuracy measured against two independent verified lender quotes for the same scenario. Each cell shows accuracy vs. Quote 1 / Quote 2.
YMT = yourmortgagetoolbox.com • WC1-WC5 = Website Calculators 1-5 • N/P = Not Provided (calculator does not calculate this)
| Metric | YMT | Website Calc 1 |
Website Calc 2 |
Website Calc 3 |
Website Calc 4 |
Website Calc 5 |
|---|---|---|---|---|---|---|
| Total Monthly Payment | 98.7% / 96.9% | 79.4% / 80.8% | 79.2% / 80.6% | 73.6% / 74.9% | 84.7% / 86.2% | 93.7% / 95.4% |
| Closing Costs | 81.6% / 86.4% | N/P | N/P | N/P | N/P | N/P |
| Prepaids | 88.1% / 74.1% | N/P | N/P | N/P | N/P | N/P |
| Total Cash to Close | 98.2% / 98.0% | 53.8% / 55.9% | 53.8% / 55.9% | 53.8% / 55.9% | 53.8% / 55.9% | 53.8% / 55.9% |
N/P = Not Provided. Accuracy calculated as: 1 − |calculator result − verified quote| ÷ verified quote. Two independent lender quotes obtained for the same scenario.
Why Closing Cost Accuracy Tells a More Complicated Story
You may notice that the accuracy figures for Closing Costs run in the low-to-mid 80s rather than the 90s. That is worth explaining, because the reason actually reflects well on yourmortgagetoolbox.com.
Because of this, most lenders deliberately over-quote these fees to protect themselves. I see it all the time: an appraisal quoted at $750 to $1,000 on a Loan Estimate when the actual cost typically runs $550 to $650. The lender is padding the number just in case. If the appraisal comes in lower, the borrower pays less than the estimate. It is standard practice, and it protects both sides from a nasty surprise at the closing table.
yourmortgagetoolbox.com uses actual typical fees, not the padded estimates that show up on formal Loan Estimates. Our closing cost figures will often run a little lower than a verified lender quote, not because anything is missing, but because we are not building in that same cushion. In practice, a buyer using our calculator is more likely to arrive at closing with money left over than to come up short.
What This Means for You
None of the five popular website calculators we tested are wrong about the math. The P&I calculation is straightforward and they all get it right. The problem is what they leave out. Closing costs. Prepaids. Accurate PMI. County-level property taxes and insurance estimates. These aren’t footnotes. They’re the difference between a buyer who is financially prepared and one who just had their excitement crushed because they can no longer afford the house they want to purchase.
The better question isn’t “which calculator gets the payment right?” It’s “which calculator tells you everything you need to know before you make one of the biggest financial decisions of your life?”
The data speaks for itself. yourmortgagetoolbox.com is the only free tool in this comparison that gives you the complete picture: full monthly payment, closing costs, prepaids, and the Total Cash to Close figure you need before you commit to a purchase. It is the only calculator that tells you not just what your payment will be, but whether you actually have enough money to buy the house.
Would you rather know now, with time to plan and save? Or would you rather find out after you’ve found your dream home, only to be let down that you can’t afford it?