Two owners on the same line of the same building spend $150,000 on the same kitchen. One of them never signs a one-page state form, so the contractor adds sales tax to every invoice and the checks total $163,312. When the job ends, that owner also throws the invoices away. The other signs a one-page state certificate before the crew starts, pays $150,000 in total, and keeps every invoice.

The first difference is the $13,312 of sales tax, and it is settled the month the work is billed. Nothing in the work made that job taxable and the other one exempt: the same kitchen qualifies either way. The second difference waits 12 years, until the sale closes, when the documented $150,000 of work stays out of the taxable gain, which at today’s rates can mean $30,000 or more in tax you don’t owe.

Neither piece of paper is complicated. One is a single page you sign, in practice before the crew starts. The other is a folder you keep until you sell. What follows is what each one does, where the line falls, and the places where owners in Manhattan lose the benefit without knowing it was available.

When the 8.875 percent comes off the bill

New York City’s sales tax rate is 8.875 percent. On a renovation invoice that bundles labor and materials, that rate applies to the whole contract price. On $150,000 it is a little over $13,000.

It applies unless the job is a capital improvement. New York State’s test asks three things, and the work has to pass all three: it makes the place worth more or last longer, it’s built in so that taking it out would damage something, and it’s meant to stay. Miss one and the job is a repair, and the tax applies to the full invoice.

The form that records this is ST-124, the Certificate of Capital Improvement. It runs one page and carries two signatures. The owner fills in and signs the customer section describing the work, and the contractor signs a section accepting it in good faith and keeps it on file as the reason no tax was collected. The contractor holds it for at least 3 years after the due date of the last sales tax return it relates to, or the date that return was filed if that is later. The certificate is not valid unless both sides are filled in. Nothing gets filed with the state.

Contractors ask for it before the first invoice, and that is the sensible way to do it, but the state’s actual deadline sits later. If your signed form reaches the contractor within 90 days of finishing the work, any later question from the state about the tax is yours to answer, not theirs. If it arrives later, the contractor stays responsible. A late certificate does not by itself make a capital improvement taxable; it just means nobody is protected by the piece of paper anymore.

The exemption does not reach the materials. Whoever buys them pays sales tax at the register, contractor or owner, and when the contractor buys them that tax is already inside the number on your contract. What the certificate removes is the second layer of tax, the one charged on the bundled invoice. Signing it wrongly also lands on you, not on the contractor. Certify a repair as a capital improvement and the state can come back years later and assess the tax against the property owner, with penalties and interest on top.

Where the line actually falls

Size has nothing to do with it. Renovating one small bathroom from nothing is a capital improvement. Replacing 40 broken faucets across a building is 40 repairs. What decides it is whether the work is permanent and integrated, or whether it puts something back the way it was.

The last row is the one that catches people. Paint by itself is a repair. Paint done as part of a gut renovation, where the room is stripped to the walls, counts as part of that improvement.

The same words, two different laws

Owners often assume one rule covers both. New York State uses the phrase capital improvement for sales tax; the IRS uses improvement when you sell. The two overlap a lot, but they are separate tests from separate governments, applied at different times.

The federal version, set out in IRS Publication 523, counts work that adds to the value of the home, prolongs its useful life, or adapts it to new uses. Additions, a new roof, central air conditioning, a modernized kitchen, new flooring, new windows. Routine upkeep does not count, and neither does fixing a leak or painting a room. But repairs done as part of an extensive remodel do count, folded into the project they belong to.

So the answer to whether painting counts is yes and no in the same apartment, depending on which law is asking and what else was happening that month. The two rules were written for different purposes, and the practical consequence is that the ST-124 you signed is not your evidence for the second one. That takes its own file.

The folder that matters 12 years later

When you sell, the tax is not on the price. It is on the gain, which is the price you get less what the place cost you. That second number is your basis, and it is not just the purchase price. It starts with the purchase price and grows by every improvement you make while you own the place.

Against that gain sits the exclusion. If it has been your main home for two of the five years before the sale, the first $250,000 of gain is free of federal tax for a single owner and $500,000 for a married couple. If your gain stays under that amount, improvements don’t change your tax, but a gain that is under the limit today may not be when you actually sell. Above it, every documented dollar of improvement is a dollar that is not taxed.

In Manhattan the $500,000 exclusion is easy to exceed, so a $150,000 kitchen with its paperwork in the file, if the kitchen is still there, is $150,000 that never enters the gain.

The catch is in that last condition: an improvement you have since replaced no longer counts. The kitchen you put in during 2012 and tore out in 2026 leaves the basis when it leaves the apartment, and only the new one counts, so an owner who has renovated twice adds just the current kitchen to the basis.

What a co-op owner keeps and what a condo owner keeps

Shares in a co-op are not real property, which changes plenty of things about a renovation. It does not change the sales tax form or the tax break at sale. Publication 523 treats a cooperative apartment as a main home like any other, so the same two-of-five-years rule and the same exclusion apply. And ST-124 is available to an owner or a tenant who contracts for the work, so a shareholder doing an alteration inside the apartment uses the same one-page form as a condo owner.

In a co-op you check the tenant box on the form rather than the owner box, and the state assumes a tenant’s work is temporary unless the papers say otherwise (Publication 862). Before you sign, check that your proprietary lease and alteration agreement say installed work stays with the apartment.

What this looks like as a habit

None of this asks for an accountant on day one. It asks for five things to exist in one place.

1. The signed ST-124, with the description of work you actually gave the contractor
2. The contract, the payment schedule, and every change order
3. Invoices marked paid, with the method of payment attached to each one
4. For a co-op or condo, the alteration agreement and the board approval, which is what shows the work was permitted and permanent
5. The DOB permit and the Letter of Completion that closes it out, which is the proof the permitted work was signed off and the document a buyer’s attorney asks for at closing

Scan all of it the week the job wraps up, while the contractor still answers the phone and can reissue anything missing. It is a bad idea to reconstruct a 2026 renovation in 2038 from bank statements, and a worse one to reconstruct it from memory.

What does not come back

A high basis is not the same thing as a high price. Documenting a $150,000 kitchen does not mean a buyer pays $150,000 more for the apartment, and in a building where most apartments have already been renovated, some of what you spend helps the apartment sell faster without raising the price. The certificate keeps sales tax off the job, and the receipts keep tax off gain you never really made.