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

# What is a Monthly Tracked User (MTU)

> One unique visitor bucketed into any experiment during a calendar month. Not one per experiment. Not one per pageview.

An MTU is a **unique visitor bucketed into any experiment during a
calendar month**. One per person per month.

<Frame caption="Billing page. Plan, usage against your caps, and the upgrade path.">
  <img src="https://mintcdn.com/abtestly/TJFfWsOMn4uzK6iy/images/billing-page.png?fit=max&auto=format&n=TJFfWsOMn4uzK6iy&q=85&s=99b61e5447d0b75f3853a13d4c83ffe0" alt="Billing page" width="2400" height="1141" data-path="images/billing-page.png" />
</Frame>

## How it is counted

Every visitor gets a stable id (a UUID in localStorage and a cookie
on your site's eTLD+1). The first time in the month a visitor is
bucketed into any experiment, they count as one MTU. Every subsequent
bucketing that month, they do not.

Counted server-side by hashing the visitor id and checking a Durable
Object per organization. There is no client-side gate a misconfigured
page can trip; the meter is entirely on our side.

## What does not count

* **A visitor on a page with no experiment.** Not counted.
* **A visitor who did not enter (allocation \< 100 %).** Not counted.
* **A blocked IP** ([Settings → Blocked IPs](/settings/blocked-ips)).
  Dropped before the MTU record is written.
* **An opted-out visitor** ([Visitor opt-out](/install/opt-out)). The
  snippet never fires.
* **Preview mode.** Preview does not send real beacons.

## MTU across multiple sites

Counted **per organization**, not per site. Same visitor on
`site-A.com` and `site-B.com` in the same org counts once.

Different organizations for the same real user count separately.
the org id is part of the hash.

## MTU across the month

Resets at the first of every month UTC. A visitor tracked in January
starts fresh in February.

## Going over

If you exceed your plan's cap:

* **Already-bucketed visitors stay bucketed.** Their variant does not
  change. Statistical validity of your running experiments is
  preserved.
* **New visitors stop being bucketed.** They see the Original.
* **You get an email** with a graph of your recent MTU consumption
  and a link to upgrade.
* **You are not auto-charged.** The bill does not change on its own.

## Downgrading mid-month

If you downgrade to a smaller plan and your current MTU is above the
new cap, the same overage behavior kicks in immediately, new
visitors stop being bucketed until next month.

Downgrading does not delete data or archive experiments. History
stays. See [refunds](/billing/refunds) for the full cancellation
shape.

## Enterprise

If your MTU is much larger than the top public plan, contact
**[enterprise@abtestly.com](mailto:enterprise@abtestly.com)**. Custom caps, custom pricing, custom
SLAs.