How to Calculate Retainage in Construction Billing
Retainage is one of the most common sources of pay application mistakes. If the numbers do not line up between line items, totals, stored materials, and payment due, reviewers notice fast. This guide explains how retainage works, how to calculate it, and how it flows through AIA-style pay applications.
What Is Retainage?
Retainage is the portion of a contractor’s payment that is held back until later in the project. In construction billing, it is often 5% to 10% of the amount earned, although the actual percentage and rules depend on the contract.
Retainage usually shows up during construction progress billing and affects the amount currently due on each pay application. It also needs to stay aligned with the pay application, the continuation sheet, and the summary page.
The Basic Retainage Formula
The key question is not just the percentage. The key question is: what amount is subject to retainage under the contract?
- Some contracts apply retainage to completed work only
- Some apply it to completed work plus stored materials
- Some reduce or release retainage after a certain milestone
Before doing any math, confirm the retainage clause and make sure it matches how the pay app is being prepared.
Example: Retainage on a Progress Payment
Here is a simple example using one billing period.
- Contract value: $100,000
- Work completed this period: $20,000
- Retainage percentage: 10%
Retainage withheld = $20,000 × 10% = $2,000
Amount earned less retainage = $20,000 - $2,000 = $18,000
If there were no previous payments and no other deductions, the payment due for that period would be $18,000.
What Happens on the Next Pay App?
Assume the next month adds another $15,000 of completed work. Now total completed to date is $35,000.
Total retainage to date = $35,000 × 10% = $3,500
Total earned less retainage to date = $35,000 - $3,500 = $31,500
This is where many spreadsheet workflows go sideways. The current payment due has to account for prior billings, prior retainage, and the new totals to date without breaking the cumulative math.
Where Retainage Appears in an AIA-Style Pay Application
In AIA-style billing, retainage usually appears in more than one place, which is why errors are so easy to spot.
1) G703 Line Items
Retainage is often applied at the line-item level on the G703 continuation sheet. That means each row can contribute to the total retainage amount.
2) G702 Summary Totals
Those line-item values then roll up to the G702 summary, where retainage affects total earned less retainage and the current payment due.
3) Schedule of Values
The math also has to stay aligned with the schedule of values (SOV) because overbilling or bad row-level math creates downstream issues fast.
Does Retainage Apply to Stored Materials?
Sometimes yes, sometimes no. The contract controls.
- Some projects apply retainage only to installed work
- Some apply retainage to installed work plus stored materials
- Some reduce retainage later in the project, but not on stored materials
If your backup shows stored materials but the retainage treatment does not match the contract, reviewers may reject the entire package even if the rest of the math is correct.
Retainage and Change Orders
Change orders complicate retainage because they affect the contract value and may change what is billable in the current period.
If the retainage percentage stays the same but the contract value changes, your cumulative totals still need to stay aligned. If the contract also changes how retainage is handled, the billing logic gets even more sensitive.
Common Retainage Mistakes That Get Pay Apps Rejected
- Applying retainage inconsistently from one billing period to the next
- Changing the retainage percentage mid-project without fixing cumulative math
- Applying retainage to stored materials when the contract does not allow it
- Failing to apply retainage to stored materials when the contract does require it
- Letting G702 summary totals drift away from G703 line-item totals
- Using spreadsheets that recast prior values incorrectly after a retainage change
- Forgetting to account for retainage when change orders are added
Why Retainage Errors Matter
Retainage errors usually do not stay isolated. One bad retainage number can affect:
- total earned less retainage
- current payment due
- stored materials treatment
- change order math
- review confidence in the whole package
That is why retainage is not just a math detail. It is a workflow detail tied directly to trust, review speed, and whether you get paid without rework.
Retainage Laws Can Vary by State
Even when the retainage math looks simple, the legal rules behind retainage are not always the same from one state to the next. Some states focus on percentage caps. Others focus on release timing, public-project treatment, or how retainage interacts with payment rights and notice rules.
That means a retainage workflow that worked on one project may not be safe to assume on another. If you work across multiple jurisdictions, it helps to understand that retainage can be both a billing issue and a legal-compliance issue.
California
Private-work limits, release timing, and stricter statutory treatment make California one of the most talked-about retainage states.
View California retainage laws →Texas
Texas retainage often gets discussed alongside owner-retainage concepts, notice issues, and broader payment-right implications.
View Texas retainage laws →Florida
Florida is especially important for public-project retainage limits, timing rules, and closeout-related payment treatment.
View Florida retainage laws →Avoid Retainage Math Errors Entirely
PayAppPro helps contractors build cleaner pay applications with cumulative math, retainage handling, stored materials support, and reviewer-friendly PDF output.