# Unix timestamp converter for Excel: the formula and a quick check

> One formula turns epoch seconds into Excel dates; here is why it works and how to handle milliseconds and time zones.

URL: https://claudegpt.si/news/unix-timestamp-converter-excel-formula  
Published: 2026-10-26T15:07:35.485Z  
Updated: 2026-10-27T15:07:37.252Z  
Author: ClaudeGPT Si Newsroom  
Section: Guides  
Topics: Excel, Unix time, Spreadsheets  
Publisher: ClaudeGPT Si

## Key takeaways

- In Excel, =(A1/86400)+25569 turns Unix seconds into a date serial number shown in UTC once the cell is formatted as a date.
- Millisecond timestamps need 86400000 as the divisor, and time zones need a fixed offset added as a fraction of a day.
- A browser converter such as AyeTab's checks single values without uploading them, and an AI assistant is better used to write the formula than to compute dates.

Excel has no built-in Unix timestamp function, but one formula does the job: `=(A1/86400)+25569`, with the result cell formatted as a date and time. For a single value, or to check the formula's output, a browser tool such as the free [AyeTab Unix Time Converter](https://app.ayetab.com/tools/unix-time) is quicker than a spreadsheet.

## Why the formula works

Excel stores a date as a count of days, with day zero set at 30 December 1899 in its default date system. Unix time stores a moment as a count of seconds since 1 January 1970 UTC. To move between the two you need two numbers:

- **86400**, the number of seconds in a day, turns seconds into days.
- **25569**, the number of days from Excel's day zero to 1 January 1970, shifts the start point.

Divide, add, and Excel sees a normal date serial number. The same formula works in LibreOffice Calc.

## Step by step in Excel

1. Put your timestamps in column A, starting in A2.
2. In B2, enter `=(A2/86400)+25569`.
3. Format B2 as a date and time: Format Cells, Custom, then a pattern such as `yyyy-mm-dd hh:mm:ss`.
4. Fill the formula down the column.

The result is in UTC. To show another zone, add or subtract hours as a fraction of a day. For UTC+2, use `=(A2/86400)+25569+(2/24)`. Daylight saving time is not handled for you, so a fixed offset is only right for part of the year in many places.

## Formula variants

| Your data | Formula |
| --- | --- |
| Seconds (10 digits) | `=(A2/86400)+25569` |
| Milliseconds (13 digits) | `=(A2/86400000)+25569` |
| Seconds, shown at UTC-5 | `=(A2/86400)+25569-(5/24)` |
| Date back to seconds | `=(B2-25569)*86400` |

If the result shows hash marks, the column is too narrow. If you get a date thousands of years ahead, your values are milliseconds and need the 86400000 divisor.

## Getting the current timestamp

The reverse formula also works on `NOW()`: `=(NOW()-25569)*86400` returns a Unix-style number. There is a catch. `NOW()` gives your computer's local time, not UTC, so the result is off by your UTC offset unless you subtract it, for example `=(NOW()-25569-(1/24))*86400` at UTC+1. `NOW()` also recalculates whenever the sheet does, so paste the value as a number if you need to keep it. The Now button in AyeTab's converter fills in the current timestamp directly, with no offset to correct.

## Checking a result without a spreadsheet

Formulas are easy to get subtly wrong, so it pays to check one row against a converter. Paste the same timestamp into AyeTab's converter and it shows the seconds, the milliseconds, ISO 8601 in UTC, your local time and a UTC date side by side. A 13-digit input is read as milliseconds automatically, which is a quick way to confirm which divisor you need.

The converter runs in the browser, with no upload and no account. That matters when the spreadsheet holds customer events or billing records. AyeTab is free, as a web app or as a [Chrome extension that replaces your new tab page](https://ayetab.com) with the same tools.

## What about asking an AI assistant

Chat assistants are good at writing the formula above and explaining it. They are less reliable at doing the arithmetic on a specific ten-digit number in their head, and a confident but wrong date is easy to miss. Let the assistant write the formula, then let Excel or a converter compute the value.

## When Excel is not the right tool

For one-off values, a converter is faster. For large exports, convert before the data reaches Excel: `FROM_UNIXTIME` in MySQL, `TO_TIMESTAMP` in PostgreSQL and `datetime(x, 'unixepoch')` in SQLite each return a proper date. Power Query and Power BI have their own date functions, which are the better choice if your data already flows through them.

## Frequently asked questions

### Does Excel have a function to convert Unix time?

No dedicated one. Divide the timestamp by 86400 and add 25569, then format the cell as a date and time.

### How do I convert a millisecond timestamp in Excel?

Divide by 86400000 instead of 86400: =(A2/86400000)+25569.

### How do I turn an Excel date back into a Unix timestamp?

Subtract 25569 and multiply by 86400: =(B2-25569)*86400. The date should be in UTC.

## Sources

- [Epoch Converter: Excel and LibreOffice Calc](https://www.epochconverter.com/), epochconverter.com
- [Unix Time Converter](https://app.ayetab.com/tools/unix-time), AyeTab
- [AyeTab](https://ayetab.com), AyeTab
- [AyeTab: Developer Utilities](https://chromewebstore.google.com/detail/hfcgbpmgokbjeiblnheamfdfbochlaah), Chrome Web Store