What a California fix-and-flip actually costs to carry
Every guide covers how to get the loan. Almost none covers the two clocks that decide whether you can pay it off inside the term — a federal resale rule that narrows your buyer pool, and a tax bill that arrives months after you budgeted for it.
The costs that show up after you have modelled the deal
Ask ten people how to underwrite a flip and you will get the same list: purchase, rehab, financing, commission, closing costs both ends. It is a good list. Every calculator on the internet implements it, including ours.
It is also a list of the costs you can see at the start.
The two that catch California investors are the ones that arrive later. One narrows who is allowed to buy your finished house, and it is a federal rule with specific date thresholds. The other is a tax bill computed on a number you have never seen, delivered months after close, that your impound account will not pay.
Neither is exotic. Both are public. Neither appears in the standard list.
Clock one: the federal resale rule decides who can buy from you
Federal regulation restricts how quickly a property can be resold to a buyer using FHA financing. The rule lives at 24 CFR 203.37a, and it has two tiers that matter to anyone holding for under six months.
Resell within 90 days of the date you acquired the property, and the mortgage is not eligible for FHA insurance at all. Not "subject to review" — ineligible.
Resell between 91 and 180 days and the property becomes eligible again, but a second appraisal by a different appraiser is required where the resale price is 100 percent or more above what you paid. In plain terms: if you double your money inside six months, a second appraiser has to agree with the first one.
Read carefully, this does not stop you selling. It changes who is allowed to buy. On an entry-priced flip — which is most flips — FHA buyers are a large share of the market, and removing them from your buyer pool for 90 days is a real constraint on the exit you underwrote.
The practical consequence is about sequencing, not about the rule. Most investors model the hold from the day the work finishes. The clock in the regulation starts from the day you acquired the property, and it runs while you are still demolishing. Model your hold from acquisition, and check where day 91 and day 181 fall relative to when you actually expect to list.
Clock two: your property tax is not the seller's property tax
This is the one that produces the surprised phone call.
Under Proposition 13, California assesses property tax on a base year value that resets when the property changes ownership. Your base year value is what you paid. The seller's assessment — the number printed on the listing, the number in the tax history, the number you copied into your spreadsheet — belongs to whatever they paid, possibly decades ago.
So the tax line in your model is very often somebody else's tax line.
The county trues this up with a supplemental assessment, authorised by Revenue and Taxation Code sections 75 through 75.72. It bills the difference between the old assessment and yours, prorated from your close date. Three things about it catch people:
It arrives separately, and later. Often months after close. On a nine-month flip it can land after you have already sold.
Your impound account does not pay it. Lenders receive a copy of the annual bill; they do not receive the supplemental. Paying it is on you, directly to the tax collector, and an unpaid one does not quietly disappear at closing.
And if you closed between 1 January and 31 May, you get two of them. That window spans two assessment rolls, so the county issues one supplemental for the remainder of the current fiscal year and a second for the whole of the next.
None of that is unusual or punitive. It is simply how the assessment cycle works, and it is entirely knowable at the point you write the offer — which is the only point at which knowing it helps.
The $500 rule that is now the $1,000 rule
A smaller one, included because the stale version is repeated almost everywhere.
California requires a contractor licence for construction work above a dollar threshold set in Business and Professions Code section 7048. For years that threshold was $500, and a great deal of investor content — including pages published this year — still says $500.
It is $1,000 now. The current statute reads that the exemption applies where "the aggregate contract price for labor, materials, and all other items is less than one thousand dollars ($1,000)", for work of a casual, minor or inconsequential nature.
The conditions matter more than the number. The exemption does not apply if the work is part of a larger operation, which a rehab plainly is. It does not apply if the person employs anyone else to help. And splitting a job into sub-$1,000 contracts to stay under the line is explicitly addressed.
For a flipper the practical reading is unchanged: your rehab needs licensed trades. The reason to know the current figure is narrower — if you are reading a guide that still says $500, you have learned something about how recently that guide was checked.
What this means for the number you put in the spreadsheet
Three adjustments, all of which you can make before you write an offer.
Model the tax line from your purchase price, not the listing's tax history. The effective rate is the 1 percent Proposition 13 base plus voter-approved local bonds and any direct assessments, so it varies by parcel — your county assessor publishes the rate for the tax rate area. If the property sits in a Mello-Roos district, that sits on top and outside the 1 percent cap.
Budget the supplemental bill separately, and assume it arrives at the worst time. If your close falls between January and May, budget for two.
Count the hold from acquisition, not from completion, and know where day 91 falls. If your projected list date sits close to it, either the timeline or the buyer pool is going to move.
None of these changes whether a deal works. They change whether the number you underwrote is the number you get, which is a different and more useful question.
Our fix and flip calculator models all three — it estimates property tax from your purchase price rather than the seller's assessment, tells you whether a January-to-May close means one supplemental bill or two, and shows the break-even interest rate for your specific deal rather than assuming a rate for you.
Sources
Everything above is public. The primary sources, so you can check rather than take our word for it:
24 CFR 203.37a, for the 90-day resale ineligibility and the 91-to-180-day second appraisal requirement.
California Revenue and Taxation Code sections 75 through 75.72, for supplemental assessments, and the State Board of Equalization's supplemental assessment guidance for the proration and the two-bill window.
California Business and Professions Code section 7048, for the current contractor licence threshold.
NexWin Capital Corp. arranges financing through third-party lenders. Nothing here is an offer or commitment to lend, and none of it is tax advice — a supplemental assessment on a specific parcel is a question for that county's assessor.
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