...
Click Set budget milestones.
For each Budget Milestone, enter a budget amount in the field. This value is cumulative, meaning that it must always represent your total budget up to that date. The Budget field is automatically filled using the amount from the topmost Budget Milestone and can’t be edited inline.
Click the Date field and select a date. The milestones need to be in chronological order, with the latest date being on top. If you enter a budget milestone with a date that’s outside the project's timeframe, the milestone is greyed out and not included in the total budget; however, you can still edit that milestone.
Optionally add a Description to help you understand what each budget milestone means when viewing your project’s Overview.
Click Add to add that budget milestone to the list.
Click Remove to remove a single milestone. If you remove the topmost budget milestone, the milestone below becomes the total Budget amount.
Click Revert to a single budget to stop using budget milestones. This deletes all your Budget Milestones data.
...