My business records were destroyed or lost in bulk — fire, flood, theft, a failed drive, a lost account — how do I reconstruct them and still prove my expenses?

In what order should the work happen?

Treat a bulk loss as triage, in this order:

1. Protect what survives, and get recovery attempted before discarding or overwriting anything.
2. If a return, an examination or a lender is waiting, secure time now.
3. Inventory what was lost and what survived, by period and record class.
4. Document the loss event, and that the lost records existed.
5. Request replacements from everyone who held your records, oldest periods first, since those age out soonest.
6. Reconstruct, and label, only what nobody else holds.
7. Log each substitution as it arrives.

Starting at step 6 is the costly mistake: recreated documents are the weakest evidence, and while you write them, copies held by others age out. With an examination open, step 2 includes engaging a representative before anything reconstructed is handed over.

What should you do in the first hours?

What to protect depends on what failed:

• Computers and drives. On Windows, Microsoft's undated Windows File Recovery help says the space a deleted file used is marked as free space that any use of the computer can overwrite, and advises minimizing or avoiding use. A failed or damaged drive is a different case: stop using it and keep it until a recovery specialist has assessed it.
• Online accounts. Do not abandon a locked account or close it before its data is recovered. Ask the provider in writing whether the data can be restored or exported and when it will be deleted, and save every lockout message and ticket as evidence of the event. A taken-over account, and recovering accounting-software data you can no longer reach, are separate questions.
• Copies elsewhere. Email, phones, cloud folders, backups, your bookkeeper's or preparer's file, and your bank, card, processor and payroll portals may all hold copies.

What if paper records are wet?

The Northeast Document Conservation Center's leaflet on wet books and records sets the priorities as removing standing water, reducing and stabilizing temperature and humidity, and isolating and protecting dry collections, and warns that if conditions are not addressed, mold can begin to develop in as little as 48 hours. For sewage-contaminated water, it says to call a professional recovery service immediately and not to handle the salvage in-house. It recommends professional dehumidification, freezing or vacuum freeze-drying for wet records or hundreds of single pages, immediate freezing for records with running or blurred inks, and contacting a conservator once items are frozen.

Photograph the damaged files where they lie before moving them, as dated evidence of the event, and keep them rather than clearing them out.

How do you inventory what was lost and what survived?

Before rebuilding anything, draw a grid: periods down the side, record classes across the top (bank and card statements, sales and purchase invoices, receipts, payroll, contractor payments, filed returns, vehicle and asset records, contracts and loans). Mark each cell lost, partly lost or intact, and note where surviving copies sit.

Note what each survivor anchors: a surviving return fixes the totals rebuilt evidence must reconcile to, and an intact month shows what a normal month contained. What survived also changes the method:

How do you evidence the loss event itself?

For travel away from home, entertainment-type activities, gifts and listed property, which includes vehicles, Treasury regulation 26 CFR 1.274-5T gives a right to substantiate a deduction by reasonable reconstruction where the taxpayer establishes that the failure to produce adequate records is due to their loss through circumstances beyond the taxpayer's control, such as destruction by fire, flood, earthquake or other casualty. So evidence both the event and that adequate records existed. An earlier log or the preparer's summary of it shows you kept logs; evidence of the lost period's own record, such as a photo of a page or messages or calendar entries referring to it, shows more.

For the event, IRS Publication 547 (2025), on casualty and theft losses of property, is a usable model: among what it says you should be able to show are the type of casualty and when it occurred, that the loss was a direct result of it, and, for a theft, that the property was stolen and when you discovered it missing. Record the same about your records, with where they were kept and which were lost, and get independent evidence:

The regulation's examples are physical casualties; whether a drive failure or an account closure counts as beyond your control is a question for a tax professional.

If only your own account exists, write a dated, signed statement now: what happened, when, where the records were, what was lost, who knew. The IRS examination manual, IRM 4.10.7, says the reliability placed on a taxpayer's oral statements must be based on the taxpayer's credibility and surrounding circumstantial evidence, so the rest of the reconstruction must lean harder on third-party documents.

Who can supply replacement records, and how far back?

A rule binding a holder, where one exists, sets what it must keep; what it sends is its own policy. Ask each in writing for its retention period by record class. Where one holder no longer keeps a period, the other side of the same transaction may: a debit-card purchase also shows on the bank statement, and a contractor payment on the Form 1099-NEC. A credit-card purchase does not; only the later card-balance payment does, showing a total, not what was bought or from whom. What no one still holds goes to reconstruction, labelled as such.

What can the IRS supply?

The IRS holds your own filings and some of what others reported:

• Business returns. The IRS page "Get a business tax transcript" offers business transcripts at no cost, through your business tax account, Form 4506-T or its business and specialty tax line: return transcripts for Form 1065 and 1120-series returns, which do not show attached documents or statements; an account transcript showing deposits and payments; and employment tax return transcripts for tax years 2023 and later. It gives no year range for the others.
• A sole proprietor's or owner's Form 1040. The IRS page on individual transcript types gives a tax return transcript showing most line items of the Form 1040-series return as filed, with its forms and schedules but not later changes, for the current and three prior tax years, and a tax account transcript generally for the current and nine prior years through Individual Online Account, with older years by Form 4506-T and availability limited in certain conditions. Its wage and income transcript, for the current and nine prior years, shows information returns filed with the IRS, may not reflect all issued to you, and is limited to approximately 85 documents.
• Copies of returns. The business transcript page says copies of original returns take Form 4506, with the processing time and fee on the form. The IRS page on reconstructing records after a disaster says a disaster designation, such as a named hurricane, written in red across Forms 4506 and 4506-T expedites processing and waives the normal user fee; its tax-records advice names only a disaster designation.
• Information returns filed through IRIS. Publication 5717, the IRIS Taxpayer Portal guide, says the portal keeps a record of completed, filed and distributed forms, shows the logged-in user's transmissions and lets you download forms as PDFs; IRIS takes nothing earlier than tax year 2022. These copies show what you reported paying, not what was bought.

Who else holds your records?

Most of the rest sits with the businesses you dealt with:

A copy invoice or statement requested as evidence is not a bill: do not pay from it, and treat any balance or payment details it shows as a separate question to settle before anything is paid. Confirm any balance or payment details only through contact details you held before the loss or can take from an independent record, such as a surviving contract, earlier correspondence or the supplier's published main number, never from the copy or the message that brought it.

What if an accountant, bookkeeper or preparer held copies?

A professional's file can replace much of the loss at once: filed returns with every schedule, workpapers, and the statements and forms you sent. Request those first, and record each as a copy from that file with the date received.

Treasury's Circular 230 rule, 31 CFR 10.28, says a practitioner must, at a client's request, promptly return the client's records necessary for federal tax obligations, and may keep copies. Those records include materials that existed before the engagement and anything you or a third party prepared at any time and gave the practitioner for the representation. A fee dispute generally does not change this, but where state law allows retention in one, only records that must be attached to your return need be returned, with reasonable access to review and copy the rest. Returns and schedules the practitioner prepared and gave you in an earlier engagement count as your records when you need them for current federal tax obligations; a document the practitioner prepared may be withheld while the fee for that document is unpaid. 31 CFR 10.28 binds practitioners; for a bookkeeper or preparer it does not cover, ask for the file in writing and check what your engagement letter says about records.

What does the IRS accept in place of a destroyed original?

The IRS examination manual, IRM 4.10.7, tells examiners that the best evidence rule requires original evidence when possible and that secondary evidence is used when originals are unavailable, its example being copies of original documents made by an examiner. Where unusual circumstances mean records do not exist, oral testimony may be the only evidence, and uncontradicted statements that are not improbable or unreasonable should not be disregarded; but oral evidence should not replace available documents and need not be accepted without further inquiry.

Where deductions rest on a substantial number of small expenditures that cannot all be documented, the manual has examiners reach a reasonable determination if there is a basis for allowance under the law and regulations, noting that close approximations can frequently be established through reliable secondary sources and collateral evidence, without relieving taxpayers of the burden of proof.

A stricter rule, 26 CFR 1.274-5T, covers travel, entertainment-type activities, gifts and listed property. Each element must be substantiated by adequate records or by sufficient evidence corroborating your own statement, and the rule supersedes the Cohan doctrine: section 274(d) contemplates no deduction on the basis of approximations or unsupported testimony. Written evidence, it says, has considerably more probative value than oral evidence alone, and more the closer in time it relates to the expenditure or use, so a statement not made at or near that time needs corroboration with a high degree of probative value.

That suggests an order of strength for what you gather:

• A copy of the original. A supplier's copy invoice or the bank's image of a cancelled check is the same document from another holder. A copy of a return shows what was claimed, not that it was spent.
• A third-party record of the transaction. A card statement line shows date, payee and amount but not what was bought or why, so pair it with something showing what.
• A corroborated reconstruction. A log or schedule rebuilt after the loss counts, under the stricter rule, only as far as its dated third-party corroboration carries it; for other expenses, IRM 4.10.7 has examiners weigh its uncorroborated parts on your credibility, and they are weaker.
• Your statement alone. This is the weakest, and for items under the stricter rule it is not enough.

No substitute is certain to carry an expense, because an examiner weighs each on its facts. What substantiates an ordinary expense in general is a separate question.

What can you assemble where no one else ever held the record?

Some records existed only with you. Build each from dated evidence and label the result as a reconstruction:

• Cash purchases. Bank statements show the withdrawals the spending came from, and a supplier's cash account, order records, photos and messages can show what was bought. Record any total resting on memory as an estimate, with its basis; for items under the stricter rule, the regulation contemplates no deduction on such an estimate.
• Documents you generated. Sales invoices can come back from sent email and customers' copies, and job files from calendars, messages and photos.
• Mileage and use logs. Rebuild day by day from dated evidence of where the vehicle went, such as customer invoices, calendars, supplier purchases on card statements and odometer readings on service invoices, as the second example below does.

Never give a reconstruction the form of the document it replaces.

How do you document the substitution?

Build the record to an auditor's test. The AICPA's auditing standards on audit documentation, AU-C 230, and on audit evidence, AU-C 500, bind auditors, not your business. AU-C 230 requires documentation sufficient to enable an experienced auditor, having no previous connection with the audit, to understand the work done, its results and the significant judgments made; an examiner, lender or accountant reviewing your reconstruction later is in the same position.

Keep a reconstruction register beside the evidence, one line per lost record or group, recording:

• The lost record or group. Record its period, class and identifying details, such as dates and document numbers. AU-C 230 has an auditor record the identifying characteristics of the items tested, or identify the population, and AU-C 500 names the class of transactions and the period that information relates to as factors that may affect its relevance.
• What replaced it. Record whether it is an exact copy, a third-party record, a reconstruction or an estimate, who supplied it, who asked and when it arrived. AU-C 505, restating AU-C 500, says the reliability of audit evidence depends on its nature and source and the circumstances under which it is obtained, and is greater for evidence from external parties and in documentary form.
• What remains unreplaced. Record what was asked of whom and the answer, such as a refusal or a period the holder no longer keeps. AU-C 230 asks for the results of the procedures performed as well as the evidence obtained.
• How any reconstructed or estimated figure was reached. Record the method and assumptions, and mark each estimate as an estimate. AU-C 230 requires significant findings or issues to be documented and gives accounting estimates and uncertainties, with the related management assumptions, as examples.

Keep each replacement exactly as received, with the email or envelope that brought it, as the record of its source and the circumstances under which you obtained it. Make each reconstruction on a separate sheet, headed as a reconstruction and dated when made, never in a form that could pass for the record it replaces. AU-C 505 says external confirmations an auditor receives directly may be more reliable than evidence the entity generates internally, and AU-C 230 that documentation prepared at the time or shortly after is likely to be more accurate than documentation prepared much later: a reconstruction made to look like a third party's record or the original would claim a source or a timing it does not have.

Keep the register and replacements together in one file, as AU-C 230 has an auditor assemble documentation in an audit file. It points to maintaining the integrity, accessibility and retrievability of documentation, and AU-C 500 notes that electronic information may be destroyed or deleted, for example if files are changed and back-up files do not exist: back up anything electronic to a separate place, and keep neither copy on the medium or account that failed. Turning the evidence into books and statements is a separate question.

What does a working inventory look like?

A landscaping business run as a sole proprietorship had its office flood in February 2026, destroying paper files for 2023 to 2025, including the van's mileage logs. The landlord's incident notice and the insurer's claim acknowledgement are on file. Three weeks in, with the oldest periods requested first, the inventory reads:

How does one expense category get from destroyed to supported?

Take the same business's van use in 2025.

Before. The trip log kept as trips happened went in the flood. The landlord's notice and insurer's acknowledgement evidence the event, and the preparer's workpapers, which summarize the 2024 log, show logs were kept.

Replacement evidence. Three third-party sources rebuild it:

• Repair-shop invoices record the odometer at 41,200 on 6 January 2025 and 63,700 on 29 December 2025: 22,500 miles between the readings.
• Customer invoices from sent email and customers' copies date 180 job visits on 150 days. Each day is mapped as one route from the yard through its jobs and back, with any same-day supplier purchase as a stop: 14,250 miles.
• Card statements show 52 purchases at a supplier 12 miles away; 30 fall on job days, and the other 22 add round trips of 24 miles, or 528 miles.

After. Business miles tied to dated evidence total 14,250 + 528 = 14,778, all on days between the readings. Treating each day as one route follows 26 CFR 1.274-5T, which lets a round trip or uninterrupted business use be accounted for by a single record. The other 22,500 − 14,778 = 7,722 miles are not claimed as business, including about 1,500 miles of bank runs and quote visits the owner recalls; bank runs are being matched to deposit and withdrawal dates on the statements, and whatever stays undated stays out.

The residual gap. The register records five points:

• The log is a reconstruction made after the flood, with each day's sources and the routing method.
• The regulation's elements for listed property include total use for the taxable period, so driving before 6 January and after 29 December is recorded as a gap, and 2025 total use as at least 22,500 miles.
• The 1,500 miles are an approximation resting on unsupported testimony, on which the regulation says section 274(d) contemplates no deduction, so they stay out unless dated evidence turns up.
• The 14,778 miles are not assured either: the regulation allows a reasonable reconstruction, and reasonableness turns on the facts.
• Nothing independent shows the 2025 log itself existed; the 2024 summary shows the practice only.

Whether recalled trips can be tied to dated evidence, and how the uncovered days affect the business-use share, are questions for a tax professional.

What should you tell whom while the rebuild is under way?

A bulk loss usually surfaces because something is due, so deal with the outside clock first:

In an examination, or where filed periods are questioned, engage a tax professional as your representative before handing over reconstructed material, so that what is produced, and how each substitute is described, is decided with advice; the IRS audits page lists a right to representation by oneself or an authorized representative. Whoever you tell, say plainly which items are copies, third-party records, reconstructions or estimates. For filed periods, the reconstruction is assembled to support the return as filed; if it shows the return was wrong, take advice on correcting it.