---
title: "Synchronizing Timer"
description: "Configure the JMeter Synchronizing Timer timers: properties, defaults, and practical usage notes for building reliable load tests."
url: https://docs.jmeter.ai/components/synchronizing-timer/
lastUpdated: 2026-10-01
source: docs.jmeter.ai
---

# Synchronizing Timer

*Part of the **Timers** category. Also documented in context in the [full Component Reference](/user-manual/component-reference/#synchronizing-timer).*

![Synchronizing Timer](/images/screenshots/timers/sync_timer.png)

The purpose of the SyncTimer is to block threads until X number of threads have been blocked, and
then they are all released at once.  A SyncTimer can thus create large instant loads at various
points of the test plan.

| Name | Required | Description |
| --- | --- | --- |
| Name | No | Descriptive name for this timer that is shown in the tree. |
| Number of Simultaneous Users to Group by | Yes | Number of threads to release at once. Setting it to `0` is equivalent to setting it to Number of threads in Thread Group. |
| Timeout in milliseconds | No | If set to `0`, Timer will wait for the number of threads to reach the value in “`Number of Simultaneous Users to Group`”. If superior to `0`, then timer will wait at max “`Timeout in milliseconds`” for the number of Threads. If after the timeout interval the number of users waiting is not reached, timer will stop waiting. Defaults to `0` |

> **Note**
> If timeout in milliseconds is set to `0` and number of threads never reaches “`Number of Simultaneous Users to Group by`” then Test will pause infinitely.
> Only a forced stop will stop it. Setting Timeout in milliseconds is an option to consider in this case.

> **Note**
> Synchronizing timer blocks only within one JVM, so if using Distributed testing ensure you never set “`Number of Simultaneous Users to Group by`” to a value superior to the number of users
> of its containing Thread group considering 1 injector only.

## Related

- [Timers, Think Time & Pacing](/topics/timers-pacing-throughput-modeling/)
- [Thread Calculator](/tools/thread-calculator/)
- [Full Component Reference](/user-manual/component-reference/)
- [Functions and Variables](/user-manual/functions/)