> ## Documentation Index
> Fetch the complete documentation index at: https://docs.alura.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Sales trend

> How est_trend_3m compares the last three months of estimated sales with the three before.

**Version 2026-10.** This page covers `est_trend_3m`, on products, shops and [trending](/features/trending) results.

`est_trend_3m` compares estimated sales in the last three completed calendar months (UTC) with the three months before them:

```text theme={null}
est_trend_3m = (sales in the last 3 months / sales in the 3 months before) - 1
```

It is a fraction rounded to four decimals: `0.12` means 12% more sales than the three months before, `-0.3` means 30% fewer. In October 2026 it compares July to September with April to June.

The monthly sales come from the monthly history described in [Sales estimates](/methodology/sales-estimates): each month's reviews divided by the shop's review rate.

`est_trend_3m` is `null` when:

* any of the six months is missing from the history, or
* the earlier three months add up to 0, so there is nothing to compare with.

It is never `0` for an unknown trend: `0` means sales were flat.

## Limits

* The latest month fills in as late reviews arrive (see [Sales estimates](/methodology/sales-estimates#known-limits)), which can pull the trend down for a few weeks after a month ends.
* Small numbers swing: a product going from 3 to 6 sales shows `1` (+100%). Trending's `rising` list ranks only items with at least 30 estimated sales a month on average for this reason.

## Version history

| Version | Change |
| - | - |
| 2026-10 | First published version. |


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