Late Fee Calculator
Find out the late fee on an overdue invoice. Choose between flat fee, monthly percentage, or daily percentage rates.
How It Works
The Late Fee Calculator helps you determine the exact penalty amount owed on an overdue invoice. Whether you charge a flat fee, a monthly percentage, or a daily percentage on late payments, this tool computes the fee based on the number of days the invoice is past due and the original invoice amount. It also calculates the total amount due including the late fee so you can include accurate figures in your collection notices and follow-up communications.
Late fees serve an important purpose in business: they incentivize timely payment, compensate the creditor for the cost of carrying unpaid receivables, and discourage habitual late payers. Including a clear late fee policy in your contracts and invoices is a widely accepted business practice and is legal in most jurisdictions, provided the fees are reasonable and disclosed upfront.
Flat Fee Formula
Late Fee = Fixed Amount (regardless of days overdue)
Total Due = Invoice Amount + Flat Fee
Monthly Percentage Formula
Months Overdue = Days Overdue / 30
Late Fee = Invoice Amount × (Monthly Rate / 100) × Months Overdue
Total Due = Invoice Amount + Late Fee
Daily Percentage Formula
Late Fee = Invoice Amount × (Daily Rate / 100) × Days Overdue
Total Due = Invoice Amount + Late Fee
Understanding Late Fee Types
There are three common approaches to calculating late fees, each with its own advantages depending on your business model and the nature of your client relationships.
Flat Fee
A flat fee is a fixed penalty amount charged once an invoice becomes overdue, regardless of how many days it remains unpaid. For example, you might charge a $50 late fee on any invoice that is not paid by the due date. This approach is simple to understand, easy to communicate, and straightforward to enforce. However, it does not scale with the invoice amount, which means a $50 fee on a $500 invoice (10%) is proportionally much higher than a $50 fee on a $50,000 invoice (0.1%). Flat fees work best for businesses with consistent invoice sizes or for smaller invoices where simplicity is valued.
Monthly Percentage
A monthly percentage fee is calculated based on the outstanding invoice amount and the number of months (or fractions of months) the payment is overdue. The most common monthly rate is 1.5%, which translates to an annual rate of 18%. This method scales proportionally with both the invoice size and the duration of the delay, making it fair for both small and large invoices. It is the most commonly used late fee structure in B2B contracts and is the default recommendation for most businesses.
Daily Percentage
A daily percentage fee applies a small rate for each calendar day the invoice is overdue. This is the most granular approach and creates a strong incentive for the client to pay as soon as possible, since the fee increases every day. A typical daily rate might be 0.05% (which equals roughly 1.5% per month or 18.25% annually). Daily rates are commonly used in industries like logistics, wholesale, and financial services where precise interest accrual is standard practice.
Examples
Example 1: Monthly Percentage
Invoice amount: $5,000. Due date: January 15. Payment received: February 14 (30 days late). Monthly rate: 1.5%. Late fee = $5,000 × 1.5% × (30/30) = $75.00. Total due: $5,075.00.
Example 2: Flat Fee
Invoice amount: $2,500. Due date: March 1. Payment received: March 20 (19 days late). Flat fee: $50. Total due: $2,550.00. The flat fee applies regardless of whether payment is 1 day or 60 days late.
Example 3: Daily Percentage
Invoice amount: $10,000. Due date: June 1. Payment received: June 16 (15 days late). Daily rate: 0.05%. Late fee = $10,000 × 0.05% × 15 = $75.00. Total due: $10,075.00.
Legal Considerations 2026
Late fees are legal in most jurisdictions, but there are important guidelines to follow. The fee must be disclosed in advance, typically in the contract or on the invoice itself. Many states and countries have usury laws that cap the maximum interest rate you can charge, so be sure to check your local regulations. As a general rule, late fees should be reasonable and proportional to the amount owed. Courts may refuse to enforce penalties that are deemed excessive or punitive. Including a clear late fee clause in your terms of service or contract is the best way to ensure enforceability and avoid disputes.
Statutory rates by jurisdiction: US states cap commercial usury between 8–24% APR (e.g., California 10%, New York 16% for unsecured debt) — see Nolo state-by-state usury reference. UK businesses can charge statutory 8% above Bank of England base rate plus a fixed compensation (£40–£100) under the Late Payment of Commercial Debts Act 1998. EU businesses use the Late Payment Directive 2011/7/EU — minimum 8% above ECB reference rate. Always confirm your local rate before drafting contract terms.
Last updated 2026-05-11 with current statutory references.
Frequently Asked Questions
What is a reasonable late fee to charge?
The most common late fee is 1% to 1.5% per month on the outstanding invoice balance, which translates to 12% to 18% annually. Flat fees typically range from $25 to $50 for smaller invoices. The key is that the fee should be reasonable, disclosed in advance, and consistent with industry norms. Excessively high late fees may be unenforceable in court and can damage client relationships.
Are late fees legal?
Yes, late fees are legal in most jurisdictions as long as they are reasonable and clearly disclosed before the transaction. Most states in the U.S. have usury laws that set maximum allowable interest rates, and many countries have similar regulations. The late fee terms should be stated in your contract, engagement letter, or on the invoice itself to be enforceable. Always consult local laws or a legal professional if you are unsure about the limits in your area.
How do I add a late fee clause to my invoice?
Include a clear statement in your invoice terms section, such as: "A late fee of 1.5% per month will be applied to all balances not paid within the agreed payment terms." It is even better to include this clause in your initial contract or engagement letter before work begins, so the client agrees to the terms upfront. Make sure the clause specifies the rate, when it begins accruing, and how it is calculated.
Is a flat fee or percentage-based late fee better?
It depends on your business. Flat fees are simpler and work well for consistent, smaller invoices. Percentage-based fees scale with the invoice amount and the duration of the delay, making them fairer for a range of invoice sizes. For most businesses, a monthly percentage (typically 1% to 1.5%) is the standard recommendation because it proportionally compensates for the time value of money and creates a growing incentive for the client to pay promptly.
Can I charge compound interest on overdue invoices?
Compound interest on overdue invoices is allowed in some jurisdictions but restricted or prohibited in others. Simple interest (where the fee is calculated only on the original invoice amount) is the standard practice and is more widely accepted. Compound interest, where the fee accrues on both the principal and previously accumulated interest, can add up quickly and may be deemed excessive by courts. If you wish to charge compound interest, it must be explicitly stated in your contract and compliant with local usury laws.
What is the UK statutory late payment rate in 2026?
Under the UK Late Payment of Commercial Debts (Interest) Act 1998, businesses can claim statutory interest at 8% above the Bank of England base rate on overdue B2B invoices. As of 2026, with the BoE base rate around 4.5%, that produces a statutory rate of roughly 12.5% APR. You can also claim fixed compensation: £40 for invoices under £1,000, £70 for £1,000–£9,999, and £100 for invoices £10,000 and above. Plus reasonable debt recovery costs above the fixed amount. These rights apply automatically unless your contract specifies a substantial alternative remedy.
When should I send a late fee notice vs sending the invoice to collections?
A typical escalation timeline is: Day 1 past due — send a polite reminder with no fee. Day 7–14 — formal late notice with applied late fee. Day 30 — second reminder with cumulative late fees. Day 45–60 — final demand letter with intent to file in small claims or send to collections. Day 90+ — refer to a collection agency (typically 20–50% of recovered amount) or file in small claims court. Adding late fees from day 1 of overdue is your contractual right, but soft escalation maintains the relationship. For ongoing clients, a phone call before applying fees often resolves the issue without straining the relationship.