Construction Budget Software: Forecast Final Cost and Cash Before They Surprise You

The problem: the budget is still the tender spreadsheet

On most jobs the budget is fixed on the day the contract is signed and then quietly abandoned. Variations are priced to the client but never added to the budget. Buying gains on one package hide losses on another. Six months in, the only forecast is the contracts manager's feel for the job, and the bank balance is the first sign that something is wrong.

For a UK contractor, cash is squeezed further by things the budget never showed: retention held until practical completion, CIS deducted from your own payments if you work as a subcontractor, and pay less notices that cut a valuation at short notice.

Why construction budgets go stale

• No owner after award. Estimating hands over a price, the site team runs the job, and nobody is named as budget holder.
• Variations live in a separate log. The value changes, the budget does not, so the forecast is wrong from the first instruction.
• Forecasts are top-down. A single "expected margin" figure, rather than cost to complete per cost code, hides where the problem is.
• Cash is forecast company-wide only, from the ledger, without the payment dates in each contract.

The six figures construction budgeting software should hold per cost code

Forecast final cost is actual plus committed plus cost to complete on the uncommitted work. Comparing it with the revised budget gives the forecast variance, which is the number a director needs every month.

Six steps to a budget that stays current

1. Load the tender by cost code into the system at award, with contingency held as its own line.
2. Name a budget holder per job, usually the contracts manager or QS.
3. Add every variation to the budget when instructed, with an estimated cost, and update it when priced and agreed.
4. Commit cost through orders so the system knows what has been bought.
5. Each month, estimate cost to complete for each code still open. The software does the arithmetic; the judgement stays with the budget holder.
6. Turn the forecast into cash using the contract's valuation dates, payment periods and retention.

Cash flow forecasting with UK payment rules built in

A cash forecast is only as good as its payment dates. Under the Housing Grants, Construction and Regeneration Act 1996, every construction contract must set when payments become due and a final date for payment (s110). The payer must give a notice within five days of each due date stating the sum and how it was calculated (s110A).

They must pay that sum by the final date unless they give a pay less notice within the agreed period (s111 as substituted). If they still do not pay, you can suspend work after giving at least seven days' notice (s112).

Good budgeting software stores those terms per contract, so the forecast knows that a valuation on the 25th becomes cash on, say, the 22nd of the next month, not "in about 30 days".

Worked example: one month's valuation turned into cash

Illustrative figures for a specialist subcontractor, CIS-registered at 20%, on a contract with 5% retention and a 30-day final date for payment.

Of £80,000 valued, about £66,900 arrives as cash this month. The £9,120 is recovered later through the company's PAYE via its Employer Payment Summary (gov.uk), and the £4,000 waits for practical completion and the end of the rectification period. A budget that treats the full £80,000 as cash will overstate the bank position every month of the job.

Managing variations inside the budget

Variations are where most construction budgets lose touch with reality. A workable process:

• Every instruction gets a number and a status: instructed, priced, submitted, agreed, rejected.
• The estimated cost enters the budget at "instructed", so cost to complete includes it from the start.
• The value enters the forecast only at "agreed", or at a cautious percentage before that, decided by policy rather than optimism.
• A monthly list of variations instructed but not agreed, with their cost, goes to the director with the forecast.

From job forecasts to a company cash view

Directors and banks look at the company, not the job. Once each job has a monthly forecast of value, cost and payment dates, the company cash view is the sum of them plus overheads, VAT and PAYE:

• Receipts by week from each contract's valuation cycle, after retention and CIS.
• Payments to subcontractors on your own final dates for payment, after the retention and CIS you deduct.
• Tax: the CIS you deducted goes to HMRC monthly, and reverse charge changes the VAT you collect from customers, so model VAT per contract rather than as a flat 20%.
• Retention releases on their expected dates, held back if practical completion slips.

A view built this way shows a cash dip three months out, while there is still time to chase a retention release, agree a payment schedule or change the start date of the next job.

What Odoo does for construction budgeting

Odoo's analytic budgets set a budget per analytic account, such as a job or cost code, and the budget report compares it with actual figures. The committed column adds confirmed purchase orders that are not yet billed, and revising a budget creates a new version while marking the old one as revised, which gives a record of budget changes (Odoo documentation).

The documentation does not describe a cost-to-complete input per cost code or a contract-based cash flow forecast. For contractors we add both: a monthly forecast screen for the budget holder, and a cash forecast that reads valuation dates, payment terms, retention and CIS from each contract. The job cost side is covered on our construction job costing page.

How to measure whether budgeting is working

• Forecast accuracy: forecast final cost at the halfway point against the final account.
• Cash forecast error: forecast versus actual bank receipts, month by month.
• Unbudgeted variations: count of instructions with no cost in the budget.
• Retention outstanding past release date.
• Time to produce the monthly forecast across all jobs.

Mistakes in construction budgeting

• Spending contingency without approval, so it disappears into the actuals.
• Forecasting cost to complete as "budget less actual", which assumes the rest of the job goes to plan.
• Counting gross valuations as cash, ignoring retention and CIS.
• Missing a pay less notice deadline on your own subcontractors, then paying a sum you dispute.
• Keeping budgets in a tool that cannot see orders, so committed cost is guessed.

Where Devvista fits

Devvista is an official Odoo partner that sets up construction budgeting software for UK contractors in Odoo, from tender budgets and variation tracking to cost-to-complete forecasts and cash flow based on Construction Act payment dates. We work remotely with UK firms, and our Odoo work is under NDA.

Good fit: contractors who already track costs and want forecasts directors trust. Not a fit: firms looking for a standalone estimating tool. Next: the full construction ERP picture, construction accounting software options, our Odoo implementation and custom software development services, how Odoo is priced, or the UK hub.