How Much Interest Can You Charge on Unpaid Invoices?

There is no single global number. How much interest you can charge on an unpaid invoice normally comes from one of three places: the rate written into your own contract, a statutory default rate set by the law where you and your customer operate, or a combination of the two. In many countries the statutory default for business-to-business debts sits somewhere in the region of 8–12% per year, but that figure varies widely by jurisdiction, depends on whether the customer is a business or a consumer, and is sometimes calculated as a central bank base rate plus a margin rather than a fixed number. Before you bill anyone for interest, find your actual figure in your contract or in your country's official late-payment source.

The three sources of your interest rate

Your contract, first. If your agreement or terms of service state a late-payment interest rate and when it starts, that's usually what governs — as long as it isn't so high it becomes unenforceable. A rate like "1% per month on overdue balances" or "8% per annum above the base rate" is common. The rate, the start date and the compounding method should all be written down, because a vague "interest may be charged" clause gives you almost nothing to point at later.

Statutory default rates, second. Where the contract is silent, many jurisdictions impose a default rate by law. The mechanics usually look like this: you get a payment period (often 30 days, sometimes 60), interest starts running the day after the due date, and the rate is either a fixed percentage or a published base rate plus a fixed margin. Some rules also allow a fixed compensation fee on top of the interest. These rules differ country by country and frequently have separate regimes for consumer and business customers.

Regulation as a cap, third. Even when your contract names a rate, the law may limit it. Some places cap late-payment interest outright; others treat an excessive rate as a penalty and refuse to enforce it. If you're unsure, assume the enforceable rate is the lower of your contract rate and whatever your jurisdiction allows.

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When interest can actually start

Interest generally can't be charged until payment is genuinely late. The sequence is: you issue the invoice with a due date, the due date passes, and interest begins to accrue the following day. Some rules add a short grace period after the due date before interest kicks in; others don't.

This means the fastest way to make interest chargeable is to make the due date unmistakable. Put the payment terms and the due date on the invoice itself, not just in an email thread — a client who genuinely lost track can't argue they never knew the deadline. If you haven't yet set terms, a step-by-step guide to how to create an invoice walks through the fields that matter, and freelancers just starting out will find the specifics in invoicing for freelancers.

Ready to try it? Create a professional invoice in under two minutes with Invoala's free invoice generator, no sign-up and no watermark.

Example: charging 1% monthly interest on a $2,400 invoice

Say you invoice a business client $2,400 with 8% sales tax, so the invoice total is $2,400 + ($2,400 × 0.08) = $2,592. Your terms say net 30, and your contract states late payments accrue interest at 1% per month, calculated on the outstanding balance.

• Invoice total: $2,592
• Due date: 30 days after issue, say 1 March
• Client pays on 1 June — 92 days late, or roughly 3 months

Using simple monthly interest on the unpaid balance: 1% × 3 months × $2,592 = $77.76 in interest, bringing the amount outstanding to $2,669.76.

Now the same invoice with no contract clause, in a jurisdiction whose default is 8% per annum simple interest: 8% × (92 ÷ 365) × $2,592 ≈ $52.27. Notice two things. First, the contract rate usually beats the statutory default, which is a reason to write one. Second, whether you compound monthly, charge a fixed compensation fee, or use a daily rate changes the total — so decide the method up front and state it plainly on the invoice. If you used free downloadable invoice templates and a client still hasn't paid, the interest is a line you add to a new "overdue" invoice or a formal demand, describing exactly how you calculated it.

Photo by Andreea Avramescu on Unsplash

How Invoala helps you set this up and chase it

Interest only works if the invoice itself is unambiguous and the follow-up actually happens. Here's the practical sequence:

1. Generate the invoice with clear terms. Use the free invoice generator: fill in the form, add your line items, tax and the payment terms — including any late-payment interest note — and download an A4-accurate PDF. No sign-up, no watermark, and the due date is on the document where your client can see it.

2. Record how long you'll wait. Set the payment term (say, net 14 or net 30) so the due date is calculated and visible rather than implied.

3. See which invoices are actually late. Tracking which invoices are paid, due or overdue means you know the exact number of days a balance has been outstanding — which is the number you multiply your rate by.

4. Follow up before it escalates. Automated payment reminders follow up on unpaid invoices, so you're not relying on memory. A firm reminder on day 31 is usually cheaper than a legal letter on day 120.

5. Quote the number, then decide. If the client still hasn't paid, reissue with the original total plus your calculated interest, and state the rate, the period and the amount — a client is far more likely to pay a figure they can verify.

Invoala is free to use for this; there's an optional upgrade if you want more, described on the pricing page.

Practical guardrails before you charge interest

• Check the official source for your rate. Government business portals, tax authorities and small-claims guidance publish the current default rate and any cap. Rates change, so a number copied from a forum a few years ago may be wrong.
• Make it proportionate. A small interest charge on a genuinely late invoice is normal commercial practice. A rate that dwarfs the original debt invites a dispute you'll probably lose.
• Keep the paper trail. Reminders, statements and a final demand showing the calculation make the charge look routine rather than punitive — and if it ever goes further, that trail is what you'll rely on.
• Decide whether to enforce it. Many businesses charge interest only when the relationship has already gone wrong, or waive it as a goodwill gesture once payment lands. That's a commercial call, not a legal one.

The short answer

Your interest rate is whatever your contract says, or — if the contract is silent — the default rate the law of the relevant jurisdiction applies to late payment, subject to any statutory cap. In practice that's often somewhere around 8–12% per year for business debts, but you must confirm your own figure with the official source, because it depends on the country, the type of customer and the wording of your terms. State the rate and start date before the invoice is ever late, apply it only from the day after the due date, and show your arithmetic.

This article is general information, not tax, legal or financial advice. Rules, rates and deadlines vary by country and change over time. Check with your tax authority or a qualified professional before acting on anything here.