You already filed your 2025 return. Cost segregation is still on the table.

No, it is not too late. If you bought a rental in 2025 and filed your return without a cost segregation study, the deduction is not gone. If you extended and then filed early, you have until October 15, 2026 to file a superseding return that replaces the original outright. Past that date, an amended return is generally available while the refund window stays open. For a property in its first year, filing rarely settles the depreciation question.

Is it too late to do a cost segregation study for 2025?

Not if the property was placed in service in 2025. Two routes exist, and which one you are on depends on a date rather than on the property.

If you filed Form 4868 and then filed your 1040 before the extended deadline, anything you file on or before October 15 is a superseding return. The IRS treats it as the return — not as a correction to one. That is the cleanest version of this, and it is the reason the next two weeks matter.

If you never extended, or October 15 passes, it is an amended return instead. Slower and more visible, but real: the ordinary window is three years from filing, or two years from when the tax was paid, whichever is later.

What makes a superseding return better than amending?

Processing and posture. A superseding return goes through as the original filing, so the refund follows the normal cycle instead of the amended-return queue, which routinely runs several months. It also reads as a filing rather than a correction.

The other reason October 15 is a real line rather than a soft one: some elections have to be made on a timely-filed return, extensions included. A superseding return still counts as timely. An amended return filed in December does not.

Does this count as a change in accounting method?

Generally not, when the property is in its first year. A depreciation method is not treated as adopted on the strength of one return; it takes consistent treatment across two consecutively filed returns. So picking up the 5-, 7-, and 15-year classes for a property first placed in service in 2025, on a superseding or amended 2025 return, is ordinarily a correction to that first year rather than a method change.

It is also why waiting is expensive. Once 2026 is filed on the 27.5-year-only schedule, the same fix stops being a simple correction, and prior-year depreciation becomes a conversation for your CPA. The cheap version of this fix has a deadline.

One thing that can block you: electing out of bonus depreciation.

Check the original return for an election out of bonus depreciation. Those elections are made by class on a timely-filed return and are generally irrevocable without IRS consent. If your preparer elected out for 5-year property in 2025, a study that reclassifies $90,000 into that class produces no first-year write-off.

Most returns that never contemplated a study carry no such election — the short-life classes were never on the schedule to elect out of. It takes a minute to confirm and it changes the whole answer.

A worked example: a $465,000 duplex, filed and then fixed.

Say you went under contract on a duplex in March 2025, closed in May, and had it rented in June. Purchase price $560,000, $95,000 to land, leaving a depreciable basis of $465,000. Your return went out in April 2026 with the whole $465,000 on the 27.5-year line: first-year depreciation about $9,160, using the mid-month convention for a June in-service date.

Now run the study. A typical residential result reclassifies around 21% of basis — call it $97,650 — into 5-, 7-, and 15-year property: appliances, carpet and vinyl, cabinetry, dedicated circuits, fencing, paving, landscaping. Because the duplex was acquired (contract signed) and placed in service after January 19, 2025, 100% bonus depreciation applies to that entire slice in year one. The remaining $367,350 of building depreciates normally, adding about $7,240.

First-year depreciation with the study: about $104,890. Against the $9,160 already on the filed return, that is roughly $95,700 of additional first-year deduction — worth about $30,600 in federal tax at a 32% marginal rate, before any state effect. On a superseding return that is a refund on the normal cycle rather than a number you carry into next April.

Will the refund actually show up?

That depends on what the loss can offset, and it is worth settling before you order anything. A $95,700 deduction on a long-term rental is a passive loss for most owners, deductible against passive income or suspended until you have some — the limits are in our note on passive losses. Short-term rental owners who materially participate, and real estate professionals, are in a different position.

Suspended losses are not wasted; they carry forward and release on sale. But a refund this winter and a deduction available in 2029 are different propositions, and worth telling apart before the study rather than after.

What to do in the next two weeks.

Four things. Confirm with your preparer whether you extended; that single fact decides superseding versus amended. Check the 2025 return for an election out of bonus depreciation. Confirm the placed-in-service date used; it drives the convention and the first-year number, and it is wrong more often than people expect (the rules are here). Then pull together closing statement, depreciation schedule, and photos — the full list is in what a study needs from you.

If you are still on extension and have not filed at all, the timeline is easier — that is the extension-deadline piece. Either way, a study documented to the IRS Audit Techniques Guide and backed by a clean fixed-asset schedule is what keeps the position audit-ready.

The savings estimate takes about two minutes and runs off your actual basis rather than a guess. If a study will not pencil on your property, we would rather tell you now than in November.