Construction Payment Schedule Calculator
Build a milestone payment schedule for an Australian construction contract — including mobilisation, progress payments, retention, GST and the final retention release.
General tool only. This calculator gives estimates based on the values you enter. Always check your contract terms and any state-specific rules before relying on the figures.
Select your state or territory
Using Australia-wide general calculation
General calculation applicable across Australia.
Include GST
10% on tax invoice
Retention is usually withheld from claims and released later depending on the contract.
Use custom milestones
Edit names, percentages and due dates row by row. Percentages must total 100%.
Payment schedule
Enter your contract value and schedule details to generate a payment schedule.
Summary
Enter your contract value and schedule details to generate a payment schedule.
How it works
Behind the numbers
The calculator splits the contract value across the milestones you set. Mobilisation is paid at the start, progress payments are spread across the build period, and substantial completion is paid near the end.
Retention is held back from each progress payment up to the cap (typically 5%). Half is usually released at practical completion and the rest at the end of the defects liability period.
Formula
The maths, written out
Gross milestone = Contract × Milestone% Retention = Gross × Retention% Net per claim = Gross − Retention GST = Net × 10% (if applicable) Total retention = Contract × Retention%
Worked example
A quick scenario
A $820,000 build with 10% mobilisation, 4 progress payments at 20%, 10% completion and 5% retention generates 7 schedule entries that sum to $820,000 net (or $902,000 inc-GST). Of the $41,000 retention held, the schedule shows a single Final Retention Release row — typically split 50/50 ($20,500 at practical completion, $20,500 at final) as the timeline below illustrates.
Frequently asked
What is a construction payment schedule?
A payment schedule sets out the milestones, percentages, and timing of payments under a construction contract. It also typically lists retention amounts held back at each claim.
How is retention usually calculated?
Retention is most commonly 5% of each progress payment, capped at 5% of the contract value. Half is often released at practical completion and the rest at the end of the defects liability period.
Do I include GST in the schedule?
It is common to show amounts ex-GST in the schedule and add GST on each tax invoice. This calculator lets you toggle GST on or off for both views.
Can I add custom milestones?
Yes — turn on “Use custom milestones” to edit the rows directly, including milestone name, percentage and due date.
Is this calculator legal advice?
No. It is a general planning tool. Always check your contract and state-specific requirements with a qualified adviser before relying on the figures.