Unique visitor

Updated 2026-11-02

Definition

A unique visitor is one browser counted once in a given period, however many times it visits. Analytics tools usually identify it with a cookie or similar ID.

The name is a little misleading. A unique visitor is a browser, which is close to a person but not the same thing. One person on a laptop and a phone counts as two. Two people sharing a computer count as one.

Example

This example uses made-up numbers. In one week:

• Ana visits five times from a laptop.
• Ben visits once from a phone and once from a work computer.
• Carla visits once, in a private window, and again in a normal window.

Tracking counts Ana as 1, Ben as 2 and Carla as 2. That's 5 unique visitors for 3 people.

Time periods matter too. Someone who comes on Monday and Tuesday counts once per day in daily reports, and once in a weekly total. So you can't add daily visitors together to get a monthly total.

What changes the count

Clearing cookies creates a new visitor. So does a new device or browser. Browser limits on cookie lifetime can also split one person into two over time. An ad blocker can remove a visitor entirely.

How Headstream measures it

Headstream counts distinct browsers using a hs_vid first-party cookie that lasts up to 400 days, with a copy in local storage. If neither store is available, it derives an ID from the request. The script sets the cookie on your apex domain, so a visitor stays the same across subdomains.

Visitors are labeled an estimate. Bots and excluded traffic are left out. Once someone is identified by email, their browsers link to one person for attribution, though the visitor count still counts each browser separately. The methodology page explains more.