A project budget is an estimate of costs, expressed in a format the finance department will accept, with enough contingency to survive reality. If estimating is predicting the future, budgeting is putting a price tag on that prediction and defending it to people whose entire job is questioning price tags.
What goes into a budget
Labour costs are usually the biggest line item. Hours × blended hourly rate for each person on the team. Don't forget the people who aren't on the project full-time - the legal review that takes two hours, the architect's three review sessions, the procurement manager who processes your purchase orders. These 'partial allocations' add up faster than you think.
Non-labour costs include software licences, cloud infrastructure, travel, training, external vendors, and the mysterious category known as 'miscellaneous' that every experienced PM budgets for because something always comes up. The printer will jam. A contractor will need onboarding. Someone will order the wrong size cables. Miscellaneous is not laziness - it's realism.
Contingency is not padding. Padding is hiding extra budget because you don't trust the estimates. Contingency is an explicit, risk-based reserve calculated from your risk register. If you identified a 30% chance that a vendor will be late, costing $10K, your contingency includes $3K for that risk. When someone asks 'what's the contingency for?' you can point to specific risks, not your gut feeling.
Tracking budget vs actuals
The golden rule of budget tracking: actual spend means nothing without context. 'We've spent 60% of the budget' sounds alarming until you add 'and we've completed 70% of the work.' Conversely, 'we've only spent 40% of the budget' sounds great until someone points out you're 60% through the timeline. The relationship between spend and progress is what matters.
Earned Value Management (EVM) is the formal way to track this. It compares three numbers: Planned Value (what you planned to have done by now), Earned Value (what you've actually delivered), and Actual Cost (what you've actually spent). The ratios give you a schedule performance index (SPI) and a cost performance index (CPI). An SPI of 0.8 means you're moving at 80% of planned speed. A CPI of 1.2 means you're getting more value per dollar than expected - enjoy it while it lasts.
For PMs who don't want to become EVM mathematicians overnight: track the simple version. Each week, update three numbers: planned spend to date, actual spend to date, and % work complete. If actual spend exceeds planned spend AND % complete is behind, you have a problem. If both are ahead, you have a different problem - but at least the team is productive.
Summary & next steps
Budgets include labour, non-labour, and explicit contingency based on risk. Track spend relative to progress, not in isolation. Earned Value Management is the formal method, but the simple version - planned vs actual vs % complete - catches most problems early enough to act.
Next: baseline and change control - the process that keeps your budget and schedule from drifting into fantasy territory.