Milestone billing means a portion of the buyer's price becomes due when a defined construction event is certified as complete, rather than on a date. It works because it aligns three things that otherwise pull apart: the buyer's willingness to pay, the developer's need for cash when spend peaks, and the site's actual progress. It fails when the milestone is written loosely enough that two people can disagree about whether it has happened.
What makes a milestone billable
A billable milestone has four properties:
- Objectively observable. "Roof casting of the 6th floor completed" is observable. "Structural work substantially advanced" is not.
- Single-event. If a milestone covers work on several floors or several trades, partial completion creates an argument. Split it.
- Certifiable by a named role. The project engineer or QS, not "the office".
- Documented at the moment it happens. A dated certificate, the measurement it rests on, and photographs. Collected a month later, it is a reconstruction, not a record.
A workable milestone set
For a ten-storey residential building on a three-year programme:
| Milestone | Definition | Share of price |
|---|---|---|
| Foundation complete | Pile cap and grade beam cast, certified | 5% |
| Structure to 5th floor | 5th floor slab cast and cured | 5% |
| Structure topped out | Roof slab cast | 5% |
| Brickwork and plaster complete | Buyer's own unit, certified | 5% |
| Handover | Possession offered after snagging | Balance |
Note that the fourth milestone is unit-specific. That is deliberate: a buyer on the third floor does not accept a bill for work on the ninth. Unit-level milestones require the system to know which units are affected by which certified event, which is exactly the link that a spreadsheet cannot maintain reliably.
The certification chain
The chain that makes milestone billing defensible runs: site measurement → engineer's certificate → milestone marked complete in the system → instalments raised for affected units → notices sent. Each step should leave a record that can be shown to a buyer who asks why they are being billed. When a buyer disputes, the answer should be a document, not a phone call from the sales manager.
The same certification discipline governs money going out. A contractor's running bill is certified on measurement before it is paid — see certifying a contractor bill — and the two certificates should be produced from the same progress record, not from two separate ones.
What goes wrong
Milestones raised in bulk after the fact. Three milestones certified in the same week, six months late, produce three simultaneous bills and a wave of complaints. Certify on the day.
No link to the collection schedule. The milestone is certified, and someone has to remember to raise the instalments. If that is a manual step, it will be late for some units and missed for others.
Silent redefinition. The site changes the sequence — say, brickwork starts before topping out — and the milestone definitions no longer describe the build. Redefinition needs the same approval as a price change, because it moves money.
When construction slips
Milestone billing is honest in both directions: if the site is six months late, the instalments do not fall due, and your collection curve moves with it. That is a real cash flow event and it should be modelled rather than discovered. What a six-month delay actually costs puts numbers on it, and developer cash flow covers how to plan around it.
What to do next
Take your current project's payment plan and mark which rows depend on a construction event. For each, write the one sentence a QS would sign. If you cannot write that sentence, the milestone is not billable yet — see how certified progress raises instalments automatically.