What Most Estimates Leave Out
Most online estimates start from the listing price and show you principal and interest, the part of the payment that pays down your loan and covers the lender's interest. That is the easy part to model, and it is only part of the bill. The real monthly cost is a stack of separate line items, and a few of them are where Bay Area buyers get surprised.
The usual estimate often misses or under-models four of them. Mello-Roos can add real money on newer homes, sometimes several hundred dollars a month. HOA dues and parcel taxes rarely show up in a quick online number. And most estimates use the prior owner's tax bill instead of accounting for supplemental reassessment. That is when the county re-values the home at your purchase price after you buy, which can raise the tax bill above what the prior owner paid. I check these on the prelim (the preliminary title report, the document that lists what is recorded against the property) before my buyers write an offer.
Calculator FAQ
Why is my real monthly payment higher than Zillow's estimate?
Because the estimate usually shows principal and interest with a rough property tax figure, and leaves out the line items that hit Bay Area homes hardest. Mello-Roos can add several hundred dollars a month on newer parcels. HOA dues, school parcel taxes, and private mortgage insurance (PMI, which applies when your down payment is under 20%) often are not included at all. And the property tax shown may be the prior owner's bill, not the higher amount you will pay after the county re-values the home at your purchase price. Add those back and the real number is higher.
What is included in the true monthly cost of owning a Bay Area home?
This calculator computes seven components: principal and interest, property tax (a 1.25% default effective rate you can edit), Mello-Roos, HOA dues, school parcel taxes, homeowners insurance, and PMI when your down payment is under 20%. Mello-Roos typically runs $1,500 to $4,000 a year on affected parcels, and $5,000 to $10,000 or more in the largest districts. School parcel taxes typically run $300 to $800 a year. A $3,000 a year Mello-Roos charge, for example, adds $250 a month on its own.
How accurate is this calculator?
The math is accounting-verified, but the results are estimates, not a quote. Every default is editable, so the accuracy depends on the numbers you put in. The real figures come from two places: your lender, for the loan terms and PMI, and the property's prelim, for the Mello-Roos and parcel taxes recorded against that specific parcel. If you want the numbers checked on a real property, send me a message and I will pull the actual figures for that home.
