# Try a change before you make it

Turn on **What-if**, or press `W`, to try planning changes without saving them. **Apply** saves them.

## Turn it on

The **What-if** button, a flask icon, is in the toolbar of list, Gantt and schedule views, and in the item details header. The mode covers the whole browser tab, and an amber frame shows it is on.

## Try changes

Change **Start**, **Finish**, **Duration (d)**, **Estimate (h)**, **Assignees** or a dependency. On a schedule, you can also set hours and reserve time. `⌘Z` or `Ctrl+Z` steps back through your proposed changes.

## Review and apply

1. Choose **Review** in the bar at the bottom.
2. Under **Your changes**, untick a change to see the plan without it.
3. Choose **Apply**. The ticked changes and what they move are saved, and the mode turns off.

## Leave without saving

**Discard** or **Discard all** turns the mode off at once. The button and `W` ask first when you have changes.

## When someone else changed the same value

**Review** shows **Changed by someone else to** and the new value. Choose **Overwrite** to keep your value. **Apply** waits until you do.

## Next

- [How what-if planning works](../../how-it-works/what-if-planning/)
- [See what a change will move](../see-what-a-change-will-move/)