Under state law, late payment interest on an unpaid invoice is calculated using a specific published rate applied to the amount due. In Kansas, a state agency that pays late is subject to a penalty of 1.5% per month on the amount due, but only if the vendor makes a written request for payment to the agency's chief executive officer, as stated by the Kansas Office of Revisor of Statutes. In New Hampshire, the annual rate for business transactions is 10 percent unless otherwise agreed upon in writing, according to the New Hampshire General Court.
Key takeaways
- Kansas agency payments: Interest penalties apply only after you send a written request to the agency's chief executive officer, as stated by Kansas Office of Revisor of Statutes.
- The Kansas rate: The penalty computes at 1.5% per month on the amount due in accordance with the section.
- The due date: Payment is due by the 30th calendar day after the agency receives either the goods or the bill, whichever date is later.
- Voucher timing: State agencies forward your request and their payment voucher to the director of accounts and reports, including the interest penalty.
- Next step: List each overdue invoice to a Kansas government agency with the date the agency received the goods or services and its bill date, take the later date plus 30 days as the due date, and send a written payment request with interest to the agency's chief executive officer.
Late payment interest calculation: the short answer
The calculation depends on which jurisdiction governs your contract and whether you have a written agreement specifying a different rate. For Kansas state agencies, the penalty is computed at 1.5% per month on the payment amount that is due, once a written request has been made. This rate applies specifically to the interest penalty under the relevant section, not necessarily to all private commercial debts. The Kansas Office of Revisor of Statutes defines this monthly penalty rate clearly for agency payments. You must verify if your client falls under this state agency classification before applying the figure.
For business transactions in New Hampshire, the default annual rate is 10 percent when interest is paid or secured. This rate applies unless the parties agree otherwise in writing. The New Hampshire General Court sets this baseline for Section 336:1 Rate of Interest. If your contract includes a written clause setting a different interest rate, that written agreement overrides the 10 percent standard. Check your contract terms first to see if a specific rate was negotiated.
These two examples illustrate how state laws provide specific numbers for calculating late charges. The Kansas rule targets agency payments, and the New Hampshire rule provides an annual baseline for general business dealings. Your final calculation will depend on the exact dates involved and the nature of the transaction. Always confirm the applicable jurisdiction before adding interest to an overdue invoice.
The parts of the charge: rate, amount due and trigger
A late payment charge rests on three components: the interest rate, the principal amount owed, and the event that triggers the penalty. Understanding these distinct elements helps you identify what applies to your specific overdue invoice before calculating a total figure.
The triggering event often requires active action from the vendor rather than automatic accrual. According to Kansas Office of Revisor of Statutes, a government agency is subject to an interest payment penalty only if the vendor makes a written request for payment in accordance with subsection (c). This means a missed due date does not by itself create the penalty: the written request is what makes the agency subject to the penalty, and the due-date rule sets when the payment is late.
Once that trigger occurs, the agency must include the penalty in its payment process. Each state agency shall forward a copy of each vendor's request for payment to the director of accounts and reports along with the voucher prepared by the state agency to make payment to the vendor, including payment of the interest penalty prescribed by this subsection. This requirement ties the penalty directly to the official payment instrument, ensuring the interest is processed alongside the principal balance.
| Component | Requirement | Publisher |
|---|---|---|
| Triggering Event | Written request for payment to chief executive officer | Kansas Office of Revisor of Statutes |
| Payment Mechanism | Voucher includes payment of the interest penalty | Kansas Office of Revisor of Statutes |
| Penalty Condition | Agency subject to penalty if vendor makes a request under subsection (c) | Kansas Office of Revisor of Statutes |
Review your invoice file to confirm whether you have sent the required written request to the agency's chief executive officer, as this step determines if the penalty provisions apply to your account.
Published rates: Kansas 1.5%, North Carolina 1% and New Hampshire 10%
State laws set specific interest rates for business transactions, with the exact figure depending on the jurisdiction and the nature of the debt.
| State | Default Rate | Scope/Exception | Publisher |
|---|---|---|---|
| Kansas | 1.5% per month on the amount due | Agency payments, after a written request | Kansas Office of Revisor of Statutes |
| New Hampshire | 10 percent annually | Business transactions; consumer credit excluded | New Hampshire General Court |
| North Carolina | 1 percent per month | Retainage exceeding owner's percentage | North Carolina General Assembly |
| North Carolina | Lower of legal or contract rate | Consumer credit awards | North Carolina General Assembly |
In New Hampshire, Section 336:1 Rate of Interest sets the annual rate at 10 percent for all business transactions where interest is paid or secured, unless the parties agree otherwise in writing ( New Hampshire General Court). This provision explicitly excludes consumer credit transactions as defined in RSA 358-K:1, V, meaning the 10 percent rate does not apply to those specific types of agreements. If you are billing a business in this state, check your written agreement first; if it specifies a different rate, that written term applies instead of the 10 percent figure.
North Carolina addresses retainage differently under G.S. 143-134.1, requiring prime contractors to pay subcontractors 1 percent per month or fraction thereof on any retainage percentage that exceeds the owner’s retainage percentage ( North Carolina General Assembly). This rule targets construction-related holdbacks rather than general invoice delays. For consumer contracts, G.S. 24-5 provides a separate standard: awards in actions involving credit extended for personal, family, household, or agricultural purposes accrue interest at the lower of the legal rate or the contract rate ( North Carolina General Assembly). When calculating interest on an overdue invoice, identify which category your transaction falls into before applying a rate.
Work out your own figure for a late agency invoice
To calculate the penalty on an overdue bill to a Kansas state agency, start with the due date. Under 75-6403, each government agency must pay the full amount due on or before the 30th calendar day after it receives the goods or services or the bill, whichever is later ( Kansas Office of Revisor of Statutes). If you and the agency agreed to different payment terms in writing, those written provisions apply instead. Identify the later of the two dates the agency received the goods or services and the bill; that date starts the 30-day clock. For help setting due dates in your own billing tool, see invoice payment schedules and due date setup.
Next, determine when the payment actually counts as made. For purposes of determining whether a payment was made in accordance with this subsection, a payment by a government agency shall be considered to be made on the date on which the warrant or check for such payment is dated ( Kansas Office of Revisor of Statutes). Look at the date printed on the warrant or check, not the date it cleared your bank account or the date the agency mailed it. This specific date tells you if the agency stayed within the 30-day window.
When computing the interest penalty due a vendor, the state agency adds seven days from the date the voucher is sent to the director of accounts and reports for payment ( Kansas Office of Revisor of Statutes). The agency adds these seven days in its own penalty computation, which is separate from the 30-day due date. Keep this distinction clear so you do not double-count time periods when working out your final figure.
Use these three data points to work out your number: * Received date: The later of the dates the agency received the goods or services and the bill. * Due date: The 30th calendar day after the Received date. * Warrant or check date: The date on the warrant or check issued by the agency.
If the Warrant or Check Date falls after the Due Date, interest may be due, but only once the vendor has made a written request for payment under subsection (c) to the agency's chief executive officer. The rate for this penalty is 1.5% per month on the amount due ( Kansas Office of Revisor of Statutes). To find your monthly figure, take the unpaid principal amount and multiply it by 1.5%. Check your contract for any written agreement that changed the standard 30-day rule before you finalize the total.
Late payment interest reference table by publisher
The table below lists the specific rates and formulas from each source publisher. Each row cites the exact provision that sets the figure, so you can verify the number against the original text before adding it to an invoice or judgment claim.
| Publisher | Jurisdiction | Rate/Formula | Statute Citation |
|---|---|---|---|
| Kansas Office of Revisor of Statutes | Kansas | 1.5% per month on amount due | 75-6403 |
| New Hampshire General Court | New Hampshire | 10% annual business rate | Section 336:1 Rate of Interest |
| New Hampshire General Court | New Hampshire | Judgments only: 26-week T-bill discount rate plus 2 percentage points | Section 336:1 Rate of Interest |
| North Carolina General Assembly | North Carolina | 1% per month on excess retainage | G.S. 143-134.1 |
Use this table to match your overdue invoice to the correct jurisdictional rule. If your contract specifies a different written rate for business transactions in New Hampshire, that agreement supersedes the 10 percent figure listed above. For Kansas agency payments, confirm the 1.5 percent monthly penalty applies after your written request is sent. North Carolina subcontractors should check if their retained percentage exceeds the owner's holdback to trigger the 1 percent monthly charge. Verify the current New Hampshire judgment rate annually using the treasurer’s determined formula.
What moves the number: written agreements, compounding and judgments
Written contracts can change the standard rules for how interest is calculated on business debts. In New Hampshire, if you agree in writing, interest on business transactions may include charging other than simple interest ( New Hampshire General Court). Without that written agreement, the New Hampshire provision for charging other than simple interest does not apply.
Kansas law handles unpaid penalties differently by automatically adding them to the principal debt over time. Any amount of an interest penalty which remains unpaid at the end of any thirty-day period after the required payment date shall be added to the principal amount of the debt ( Kansas Office of Revisor of Statutes). Once this addition occurs, interest penalties then accrue on that newly added amount.
Judgment interest rates differ significantly from pre-judgment business rates and follow specific annual formulas. In New Hampshire, the state treasurer determines the annual simple rate of interest on judgments as the prevailing discount rate of interest on 26-week United States Treasury bills at the last auction preceding the last day of September, plus 2 percentage points ( New Hampshire General Court). The treasurer must determine and transmit this rate to the director of the administrative office of the courts on or before the first day of December in each year. This sets a fixed annual figure for all judgment interest rather than a variable monthly rate. For a state-by-state walkthrough, see how to find your judgment interest rate.
South Carolina law provides a general mandate for court orders regarding money. A money decree or judgment of a court enrolled or entered must draw interest according to law ( South Carolina Legislature). For when that interest starts, see Judgment interest start date: 7 rules by state and debt.
| Scenario | Rule Change | Trigger/Date | Publisher |
|---|---|---|---|
| Business transaction compounding | Interest may include charging other than simple interest | Agreed upon in writing | New Hampshire General Court |
| Kansas penalty accumulation | Unpaid penalty added to principal amount | End of any thirty-day period | Kansas Office of Revisor of Statutes |
| Judgment interest calculation | Rate set by T-bill discount rate plus 2 points | Last auction before last day of September | New Hampshire General Court |
| South Carolina judgments | Money decree must draw interest | Enrolled or entered | South Carolina Legislature |
Today, check your written contract for explicit interest clauses before applying any default state rate to an overdue invoice.
FAQ: late payment interest on your invoices
How do I calculate late payment interest on an invoice?
Apply the state's published monthly or annual rate to the unpaid principal amount once the statutory trigger occurs. For Kansas agency payments, the Kansas Office of Revisor of Statutes specifies a penalty computed at 1.5% per month on the amount due. You must identify the correct trigger date and applicable rate before multiplying.
Does the Kansas 1.5% interest penalty apply to my invoice to a Kansas government agency?
Yes, if the agency fails to pay within the prescribed time and you submit a written request for payment with interest. The Kansas Office of Revisor of Statutes states that agencies are subject to this penalty only after the vendor makes a request in accordance with the statute. Without that specific written request to the chief executive officer, the penalty does not attach.
When does interest start on a late Kansas agency payment?
Interest can begin after the 30th calendar day following the later of the dates the agency received the goods or services or the bill, once the vendor has made a written request. The Kansas Office of Revisor of Statutes says a vendor may make a written request for payment to the agency's chief executive officer, and that request is what triggers the interest penalty. Track both the date the goods or services arrived and the bill date to determine which is later.
Can I charge compound interest on a late business invoice in New Hampshire?
Only if the parties agreed in writing to charging other than simple interest. Review your contract terms to confirm whether such an agreement exists before adding compounded figures.
What interest rate applies after I win a judgment in New Hampshire?
The rate is the 26-week Treasury bill discount rate plus 2 percentage points, set each year by the state treasurer under the New Hampshire General Court rules. It applies to judgments, including prejudgment interest, and is rounded to the nearest tenth of a percentage point.