What Is difference between budget & estimate?

Budget is basic cost approximate

Estimation is detailed cost to excute

Estimation is basic step for counting work as per CPM, which contains  some void /alternates activities. Complete analysis of manpower and material as per current Market rates.

Budget is bigger evaluation, consisting; cost controlling based on estimation along with margin to withdraw or add new but compulsory activity.

Budget:

Budget is a Planned allocation of resources.

i.e Planned Cost - Quantity x unit Cost. 

Estimate:

To analysis and calculation of Unit Cost is called Estimation.

• An estimate comes first and is generally a broad, big picture total sum used in cost/benefit analysis and strategic decision making prior to committing to a course of action.
• A budget is developed after the decision to commit is made and is generally far more detailed, broken into time periods and used to empower, control and account for operational decisions made during the actual implementation of the strategic decision.