Prompt Payment Interest Calculator
Prompt payment interest is the unpaid amount multiplied by your interest rate, prorated for each day the payment runs late. Most state prompt-payment statutes set a default rate between 0.75% and 2% per month. Enter the amount, due date, and rate below to see interest accrued, the daily cost, and the total owed.
How much is a late payment costing you?
Invoice details
The past-due principal. Don't include interest already charged.
Use the contract due date, or the statutory deadline if the contract is silent (our payment deadline calculator finds it). Set a later “through” date to project what waiting costs.
Pull this from the contract or your state's prompt-payment statute. Don't guess: the rate is the whole calculation.
What the late payment costs
45 days past due
Days late
45
Until the check clears
Interest
$1,109.59
Simple interest, 18.00% a year
Per day
$24.66
Each extra day of waiting
Total owed
$51,109.59
Principal plus interest
Every day late costs you.
That’s $24.66 a day this invoice sits unpaid. Get waivers signed in minutes, not weeks, so the clock stops sooner. Your sub signs on their phone with no account, and we remind them until it’s signed.
“The hardest part of lien management has always been chasing waivers and keeping everything organized. LienDone has solved that puzzle, and they’ve been great to work with.”
Math runs in your browser. Nothing is sent to a server until you ask for the email. Interest is computed as simple interest prorated daily; some contracts and statutes compound monthly or prorate differently, so confirm the method in your contract or state statute before invoicing. Not legal or accounting advice.
Every day late costs you. Get waivers signed in minutes, not weeks.
Start free for 14 daysSee it in about a minute
Create a project, add a subcontractor, send the statutory form for the project's state, and watch the sub sign on their phone with no account.
Why the daily number matters more than the total
Most payment conversations stall on principle: you say the money is late, they say it's processing. The interest figure changes the conversation because it moves. A $50,000 payment at 1.5% per month costs the payer about $25 every day it sits. Saying “this is costing you $25 a day and I'm obligated to invoice it” gets a different response than “please pay when you can.”
The legal footing comes from prompt-payment statutes. Every state has one for public work and most cover private construction, each naming a deadline and an interest rate for payments that miss it. The payment deadline calculator finds the due date; this one prices what happens after it. For how those deadlines play out across a project, typical payment terms for contractors walks through the Net 30 that becomes 83 days.
If the conversation doesn't move the check, the escalation path is written: a demand letter with the math, then an intent-to-lien letter, then the lien itself. Watch the clock on that last step: the lien deadline calculator shows how long you have.
Frequently asked questions
In most states, yes. Prompt-payment statutes set a default interest rate on late progress payments and retainage, typically between 0.75% and 2% per month depending on the state and whether the project is public or private. Many contracts set their own rate on top. The right rate for this calculator comes from your contract first, your state's prompt-payment statute second.
Late payment interest rules in the biggest markets
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