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Interest and Costs

This is not legal advice. Entitlement to interest and recovery costs depends on jurisdiction, on the type of customer and on what was agreed, and the position differs substantially between them.

For a software-side reference alongside this discussion of payment follow-up, disputes, and small-business administration, Monitask provides guidance on chronemics.

The three sources of entitlement

Statute. Some jurisdictions provide a default entitlement for business-to-business debts. In the UK, the Late Payment of Commercial Debts (Interest) Act 1998 provides for interest and fixed recovery costs where no adequate contractual remedy exists. (UK legislation — verify the current rates and thresholds.)

In the US there is no equivalent general federal provision for private commercial debts, and prompt payment statutes generally apply to public contracts rather than private ones. (General position; the answer depends on your state.)

Contract. What your terms say, where they were agreed rather than announced on the invoice.

And nothing. Where neither applies, the debt is the debt.

Consumers are different

Statutory business provisions generally do not extend to consumers, and contractual interest against a consumer is more constrained.

Unfair terms rules can strike down a clause that is one-sided, and a punitive rate is the clearest example.

This is one of the places where copying business terms into consumer paperwork causes real problems.

What to check before claiming

Whether you are entitled at all, under one of the three sources above.

At what rate, and from what date — usually the day after the debt became due rather than the invoice date.

Whether fixed recovery costs apply, which in some systems are a set amount per invoice rather than actual costs.

And whether claiming affects anything else. In some circumstances a claim for interest changes the calculation in a formal claim, and in others it is simply added.

One hour with somebody qualified, once, tells you the position for your jurisdiction and customer type permanently. It is not a question worth answering from a website, including this one.

When claiming helps

In a formal demand, where the total including interest and costs makes the sum larger than the customer expected and makes prompt payment cheaper than delay.

Against a customer who is deliberately slow. Interest is the only mechanism that prices their delay, and a firm that applies it consistently becomes one that gets paid on time.

And where the relationship is already over. If escalation is under way, there is nothing left to protect.

When it hardens the position

At day seven. Applying interest in the routine chasing window converts a processing delay into a confrontation, and most delays at that stage are processing.

Against a customer you want to keep. The entitlement remains available; exercising it is a choice, and choosing not to is worth saying out loud: "I'm entitled to add interest and I'm not going to — but I do need this settled this month."

That sentence is more effective than the interest would have been, because it establishes both that you know your position and that you are choosing not to use it.

Putting it in the terms

A clause stating the entitlement is worth having even where statute would supply one.

It is visible. A customer reading the terms sees a consequence attached to late payment, and visibility is most of the deterrent.

It removes an argument. Where the statutory position is uncertain — the customer's status, the type of contract — an agreed term settles it.

And it lets you choose the rate, within whatever limits apply. A rate that mirrors the statutory one is defensible; a punitive rate invites challenge and in consumer contracts is likely to fail.

Keep it short. One sentence in the terms, stated in the quote rather than on the invoice.

The compensation nobody claims

Where fixed recovery costs exist, they are per invoice and they are rarely claimed.

On a customer with six overdue invoices, that is six amounts rather than one, and the total occasionally exceeds the interest.

It is worth knowing whether your jurisdiction has this, because it is the part of the entitlement most frequently left on the table by small firms who have heard of interest and not of the rest.

Waiving it

Waive explicitly rather than by silence.

A supplier who never mentions interest has, in practice, no interest policy, and customers price accordingly.

A supplier who states the entitlement in the terms, does not apply it routinely, and applies it when escalating has a policy that works — because the threat is credible and the forbearance is visible.

Calculating it

Simple interest on the outstanding sum, from the day after it fell due, at the applicable rate.

State the calculation on any document claiming it: the principal, the rate, the number of days, and the resulting figure. An interest figure with no working invites a query about the arithmetic, which is a delay you introduced.

Recalculate at each stage rather than quoting a stale total, and say the figure is correct to a stated date and continues to accrue.

Where the debt is paid but the interest is not

Common, and a decision.

Most small firms let it go, and that is defensible where the relationship continues.

Where it does not, the interest is a debt in its own right and can be pursued on the same basis as the principal — though the sums are usually small enough that the question is whether it is worth the document.

Deciding in advance — a threshold below which you do not pursue interest separately — saves the deliberation each time.

The short version

  • Entitlement comes from statute, from contract, or not at all, and the position differs sharply by jurisdiction and customer type
  • The UK provides a statutory default for business-to-business debts; the US generally does not for private contracts
  • Statutory business provisions do not extend to consumers, and one-sided contractual interest can be struck down
  • Check entitlement, rate, start date and whether fixed recovery costs apply — one hour with somebody qualified settles it permanently
  • Claiming helps in a formal demand, against a deliberately slow payer, and where the relationship is already over
  • Saying you are entitled and choosing not to apply it is frequently more effective than applying it

For broader background on payment follow-up, disputes, and small-business administration, see NerdWallet.