Why would an accountant need the exact timestamp from a swap I did on Polygon

07 September 2026

Your accountant needs the exact timestamp because tax rules attach to moments, not to transaction hashes. The time you swapped determines which tax year it falls into, which rate schedule applies, and how long you held the asset.

Here is why the precise minute matters.

Tax year boundaries are fixed, and they are not forgiving

Most jurisdictions tax crypto disposals in the calendar year the trade happened. A swap at 11:58 PM on December 31st is last year's business. The same swap at 12:02 AM on January 1st is this year's. Your accountant does not need the timestamp to be pedantic; they need it because your tax return has a date line, and the date line must match the exchange's record.

Polygon blocks are produced roughly every two seconds, and each block carries a Unix timestamp. That timestamp is the authoritative moment of the swap. If your wallet or a block explorer shows a different time than your accountant's records, the discrepancy is a red flag for auditors. A timestamp resolves that flag before it becomes a question.

Holding period rules depend on the exact block, not the day

Many tax regimes treat short-term and long-term capital gains differently. The cutoff is often one year from the acquisition date. If you bought a token on May 14th at 3:00 PM and swapped it on May 14th the next year at 2:00 PM, you have a short-term gain. If you swapped at 4:00 PM, you have a long-term gain. That one hour changes the rate.

The accountant cannot guess which side of the line you fall on. They need the block timestamp to compute the holding period in hours, not in calendar days. Some years have leap seconds, some blocks are reorged, and some wallets display local time while the chain records UTC. The exact timestamp removes all ambiguity.

Cost basis methods require a sequence, and sequences need times

If you bought the same token in several batches, your accountant must choose which lot you sold. The most common method is FIFO - first in, first out. That requires ordering your acquisitions by time. But if two purchases landed in the same block, or if you swapped one token for another that you then swapped again an hour later, the order of events must be established from timestamps alone.

Without a timestamp, the accountant would have to assume an order. Assumptions create errors. Errors create amended returns. Amended returns create audits.

The timestamp is also the audit trail

A swap on Polygon involves a transaction hash, a wallet address, and a block number. The hash proves the transaction happened, but it does not prove when it happened to a human reader. The timestamp is the only field that ties the hash to a real-world clock. When your accountant later matches your records against the exchange's export, or against a tax software import, the timestamp is the key that joins the rows.

If you only saved a screenshot of the swap confirmation screen, that screenshot likely shows a date and time - but from your device, not from the chain. Your device clock can be wrong, or set to a different timezone, or changed by daylight saving. The block timestamp is the source of truth. The accountant wants that source, not the screenshot.

What to do now

If you have the transaction hash, you can find the timestamp on any Polygon block explorer. That is the exact number to save. If you are still on the swap confirmation screen, screenshot the block number and the timestamp if it is shown - but know that the explorer view is better.

If you have not yet swapped, and you are wondering what records to keep, the hub page titled Which swap records to keep for tax time walks through the full list. The timestamp is one item on that list, and it is the one that most people forget.

The short version: your accountant is not being difficult. They are trying to place your swap on a timeline that the tax authority will accept. The timestamp is the only proof of that placement that does not depend on anyone's memory or clock. Give it to them, and the rest of the return gets simpler.

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