Budgets and estimates have many similarities, but budgets tend to be used more in CORE for internal purposes. They are used to track hours and units in detail for your employees and show expected revenue and cost. You can also use a budget for multiple phases and convert it to an estimate for any proposed job.
Estimates are used when clients are bidding on a job. Estimates can also be assigned to multiple projects and when the bid is accepted, the estimated service hours and expenses can also be converted to a budget. Estimates are typically used for external purposes and they exclude details such as employees working on various activities.