Why budgets balloon: 6 main causes and how to keep control

Ask ten people who just finished building a house and more than half will say it "went over budget". The question is why — break down the causes and most aren't force majeure, but decisions that went wrong from the start

The top 6 causes

• 1. Changing the design during construction — The number one culprit: knocking down walls already built, moving a bathroom after the pipes are laid. Each change means paying twice: demolition + redoing How to control it: spend enough time on the design, visit show houses or use 3D images until you're sure, then "freeze the design" before work starts
• 2. A BOQ that isn't detailed, with many lump-sum items — Anything not specified = something you'll pay extra for later How to control it: Break down every lump-sum item before signing
• 3. Forgetting the budget outside the house — Land filling, fence, gate, parking, water and electricity meters, water pump, tank, power pole to the house — together often over 200,000–500,000 baht How to control it: Make two clearly separate budgets: the house, and everything outside it
• 4. Upgrading materials on the fly — You visit a tile shop and your heart melts; upgrade a little in every category and you end up over a hundred thousand without noticing How to control it: Set a single "total upgrade budget", e.g. 100,000 baht; any upgrade comes out of it, and when it's gone, it's gone
• 5. Extra work without an agreed price — "I'll add that for you" with no price attached becomes a bill at the end How to control it: Iron rule: every extra item must have a quotation and written approval before work starts
• 6. Delays — The longer it takes, the more you pay: rent while you wait, loan interest every day How to control it: Daily penalties in the contract + weekly progress tracking

Tools that help

What works best is "seeing the numbers in real time" — record every expense against the budget as you pay, not adding it up at month-end. Bhoon Kharn has a project budget system with per-category budgets, expense recording by scanning receipts, and automatic alerts when a category nears its budget, free in the project management system