Construction Contract Payment Schedule Calculator
Calculate milestone-based payment schedules for construction contracts including retainage withholding, progress payments, and final payment amounts.
Formulas Used
Mobilization Payment: Mobilization ($) = Contract Value × (Mobilization % ÷ 100)
Progress Payment Allocation: Remaining % = 100% − Mobilization % − Substantial Completion %
Each Milestone % = Remaining % ÷ Number of Milestones
Gross Milestone Payment = Contract Value × (Each Milestone % ÷ 100)
Retainage Withholding: Retainage per Payment = Gross Payment × (Retainage % ÷ 100)
Net Payment = Gross Payment × (1 − Retainage % ÷ 100)
Substantial Completion: Substantial Completion ($) = Contract Value × (Substantial Completion % ÷ 100)
Net Substantial = Substantial Gross × (1 − Retainage % ÷ 100)
Final Payment (Retainage Release): Final Payment = Σ All Retainage Withheld = (Retainage per Milestone × Number of Milestones) + Retainage on Substantial Completion
Verification: Total Paid = Mobilization + (Net per Milestone × Milestones) + Net Substantial + Final Payment = Contract Value ✓
Assumptions & References
- Retainage is withheld from progress milestone payments and the substantial completion payment; mobilization is typically paid in full without retainage withholding.
- All withheld retainage is released as a lump-sum final payment upon project closeout and owner acceptance.
- Progress payment milestones are evenly distributed across the contract duration between mobilization and substantial completion.
- Standard retainage rates range from 5%–10% per AIA Document A201 General Conditions and most state construction statutes.
- Mobilization payments typically range from 5%–15% of contract value per industry practice (AGC guidelines).
- Substantial completion payment is separate from final payment per AIA A201 §9.8 and §9.10 definitions.
- Many states have prompt payment laws (e.g., Federal Prompt Payment Act, 31 U.S.C. §3901) requiring payment within 14–30 days of approved pay application.
- Retainage reduction after 50% project completion is permitted or required in many jurisdictions — consult your contract and local statutes.
- This calculator does not account for change orders, disputed amounts, stored materials, or lien waivers.