The Prompt Payment Interest Calculator estimates days late and simple daily interest for construction payment delays. It uses state prompt-pay day counts from the stored payment dataset where available, but requires the user to enter the applicable annual interest rate and does not invent statutory interest rates.
Prompt Payment Interest Estimate
Estimate how many calendar days a payment is late after a selected state deadline, then calculate simple daily interest using the annual rate you enter.
State rules come from the stored payment dataset.
Use this when you already know the due date.
Used only if due date is blank and the selected rule has numeric prompt-pay days.
Required. Enter the rate that applies to your statute or contract.
Result
Statutory prompt-pay days
7 days
Resolved due date
Not calculated
Days late
Not calculated
Estimated interest
Enter due date and rate
Enter a payment due date, or enter an invoice date for states and project types with a numeric prompt-pay deadline.
Estimate formula: amount owed x user-entered annual rate x days late / 365. This is simple annual interest prorated daily over 365 days.
California has strong prompt pay laws for both public and private projects. Public retainage capped at 5%; private retainage capped at 5% (Civil Code §8822). Mandatory 20-day preliminary notice for subs and suppliers to preserve lien/bond rights.
Related guide
Construction Prompt Payment Guide
Review payment deadlines, retainage context, and collection steps before relying on an estimate.
Example
A California public-project subcontractor has a $50,000 invoice and wants a rough simple-interest estimate after a 7-day statutory deadline.
How to Use This Tool
- 1Choose the state and whether the job is public or private.
- 2Enter the date payment became due, or enter an invoice date and let the tool apply the numeric prompt-pay days only when the dataset has them.
- 3Enter the amount owed and the annual interest rate that applies to your statute or contract.
- 4Review the days-late count, simple daily interest estimate, state note, and limitation language before taking action.
How to Apply the Results
Use the estimate as a collection planning aid, not as a demand letter amount. If the selected state has no statutory prompt-pay deadline for that project type in the dataset, verify the contract and statute before calculating from an entered due date.
Frequently Asked Questions
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