Why is my construction project over budget?
Compare the current forecast with the original budget on the same scope and cost basis. Then separate unavoidable exposure from decisions you can still change.
by Jack Butler-Kettle · About 4 min readShare
What does this mean for me?
An overrun can come from omitted work, design changes, allowance shortfalls, price movements, delay or duplicated figures. Several causes may be present together.
Money paid to date is not the forecast final cost. Unpaid commitments and unfinished work can create a substantial remaining exposure.
The RICS cost-reporting guidance provides a framework for reporting costs and changes. Use a consistent reporting date and explain the basis of each amount.
What do I need to do?
1. Recover the original budget basis
Find the approved budget, design issue, pricing date and exclusions. Identify whether fees, tax, external works and risk were included.
Compare the same scope with the current forecast. A build-only allowance cannot fairly be compared with a total including land and professional costs.
Keep both figures visible where the original budget omitted necessary work; do not rewrite history to hide the difference.
2. Reconcile paid, committed and remaining work
Build a package list showing the agreed order value, changes, expenditure and remaining forecast. Add unplaced work and unresolved scope.
Avoid adding paid amounts to full contract commitments when those payments are already part of the commitment. Remove replaced allowances.
Use the cost-at-completion guide to distinguish the forecast from a cash-flow report.
3. Explain each movement from the budget
Give every material movement a cause, source and status. Separate approved changes, pending changes, errors, scope omissions and remaining risks.
Ask for support where a figure is only an assertion. Uncertain costs should remain visible with a stated assumption or range.
If a builder increased a fixed quotation, use checking additional charges before treating every increase as agreed.
4. Price realistic decisions before making them
Identify work already committed and work still open to change. Price each option including cancellation, redesign and programme consequences.
Removing a necessary allowance only lowers the spreadsheet total. It does not remove the obligation or cost.
Use value engineering to test alternatives against essential requirements. The designer must assess technical acceptability.
5. Approve a revised forecast and monitor it
Record the accepted scope, revised budget, remaining risk and actions. Give each outstanding decision an owner and date.
Review changes before instruction and reconcile subsequent forecasts to this baseline. Keep funding dates separate from total expenditure.
Our Project cost reporting service reconciles commitments, changes and remaining allowances into a forecast final construction cost.
Sources
Forecast final cost report
Remove overlap between actual cost, commitments and remaining estimates. Record the cutoff date and the source of each remaining-cost forecast.
Free blank template for your own project. The completed example is shown below. No email address required.
View the completed example
Completed fictional example
Westhaven refurbishment · 14 October 2026 · Version 1.0
Forecast final cost report
Scroll across if needed to read the whole record. A dash means no value has been entered.
| Package / cutoff | Budget (£) | Cost to date (£) | Unpaid commitments (£) | Uncommitted remaining (£) | Forecast final (£) | Forecast over budget (£) | Basis / action |
|---|---|---|---|---|---|---|---|
| Partitions / 30 Sep | £100,000.00 | £60,000.00 | £25,000.00 | £20,000.00 | £105,000.00 | £5,000.00 | £5,000 forecast overrun; review remaining labour |
| Ceilings / 30 Sep | £80,000.00 | £30,000.00 | £40,000.00 | £5,000.00 | £75,000.00 | -£5,000.00 | £5,000 below budget; scope and accruals checked |
Positive variance means forecast over budget. Exclude already-recorded accruals from unpaid commitments to avoid counting them twice.