Dunning & default interest for Swiss SMEs: why open invoices cost you more than the interest (2026)
Calculate default interest under OR Art. 104 correctly, document dunning stages cleanly, protect liquidity: the practical guide to dunning for Swiss SMEs. People decide, the assistant does the legwork.
In short: The 5 % default interest under OR Art. 104 is rarely the real problem. The real problem is the time that gets lost in the dunning run — and the liquidity that sits too long in open receivables. This guide shows you how to calculate default interest correctly, document dunning stages defensibly, and prepare the whole process to the point where all that remains is a human approval.
The problem nobody likes to look at
Most Swiss SMEs don’t have a margin problem. They have a timing problem.
An invoice for CHF 8’000 paid 60 days late doesn’t primarily cost you the default interest — at 5 % p. a. that’s around CHF 66. It costs you the CHF 8’000 that is not in your account during that time, while salaries, suppliers and VAT keep coming due.
And it costs you something that never appears in the books: the hours someone spends going through open items, checking who has already been dunned, calculating the correct default interest, drafting a polite but firm letter, and not being entirely sure at the end whether the second reminder actually went out.
That is where the SME loses money — not on the interest rate.
What the law actually says (OR Art. 102 & 104)
Before talking about software or assistants, a quick look at the legal basis — because many SMEs either dun too timidly or in a form that won’t hold up.
Default begins (OR Art. 102): If a claim is due and not paid, the debtor enters default through a reminder. If the contract or the invoice names a specific payment date (e. g. «payable by 30 April»), in some constellations default begins even without a reminder, simply by the date passing. In practice, you send a reminder anyway — properly documented is always better.
Default interest (OR Art. 104): Once in default, you as the creditor owe nothing; the debtor owes you default interest of 5 % per year, unless a higher rate was contractually agreed. The interest runs from the day default begins until payment.
Important for the calculation: Default interest is calculated on the outstanding gross amount, on a per-day basis. The customary method in Switzerland uses 360 days per year (commercial interest calculation).
Default interest = Amount × 5 % × (days in default / 360)
An example: CHF 8’000, 60 days in default.
8’000 × 0.05 × (60 / 360) = CHF 66.67.
Sounds small. And that is exactly the point: the interest is not your return, it’s your leverage. The real value lies in the invoice being paid sooner.
The customary Swiss dunning practice (3 stages)
There is no statutory requirement on the number of reminders. But a three-stage approach has become the de facto standard, and it holds up before any later debt-collection proceedings:
1. Payment reminder (friendly, often free of charge). Neutral tone — «presumably overlooked». No default interest, no reminder fee. Goal: preserve the relationship, trigger payment.
2. Dunning letter (firm tone, default interest starts to bite). Clear deadline, reference to default interest, possibly a moderate reminder fee (in practice often CHF 20–40, if covered by contract or general terms).
3. Final reminder / debt-collection warning. Final deadline, warning of debt-collection proceedings. From here, the case is often passed to a debt-collection agency or directly into formal proceedings.
The crux is not which stage you write — it’s that all three stages happen consistently, on time, and traceably. That is exactly what breaks down in daily life as soon as there are more than a handful of open items.
Where the time really goes — a worked example
Take a typical Swiss SME with around 40 open receivables per month, of which experience suggests 8–12 need a reminder.
Note: the figures below are a transparent model based on industry-standard assumptions, not a measured value from a single customer.
| Step in the dunning run | Time per case (manual) | 10 cases / month |
|---|---|---|
| Review open items, reconcile incoming payments | 6 min | 60 min |
| Determine the correct dunning stage | 3 min | 30 min |
| Calculate and verify default interest | 5 min | 50 min |
| Draft and lay out the dunning letter | 8 min | 80 min |
| Send, file, mark as «dunned» | 4 min | 40 min |
| Total | 26 min | ≈ 4.3 h / month |
Roughly 4 hours per month, or about 50 hours per year, for a process that is almost entirely rule-based. At an internal hourly cost of CHF 60, that’s around CHF 3’000 per year — for work that takes very little judgement but is easily error-prone.
On top of that comes the invisible item: every day a reminder is not sent is one more day of tied-up liquidity.
The decisive point: people decide, the assistant does the legwork
This is where we at hegyon.ai think differently than a classical ERP.
An ERP module gives you a screen in which you trigger the reminder yourself. You have to know which customer is up, which stage, and you click through the process. The tool waits for you.
An operational AI assistant turns this around. It prepares the entire dunning run and presents it to you decision-ready:
- It recognises which invoices are overdue, because it has already reconciled incoming payments (e. g. via the CAMT import).
- It determines the correct dunning stage per case based on the existing reminder history.
- It calculates default interest under OR Art. 104 on a per-day basis.
- It drafts the dunning letters in the right tone and language.
- It puts the result in front of you as a list of «To approve».
And then — this is deliberate — nothing happens until a human decides. You see the ten prepared reminders, you check the two delicate cases (the long-standing customer where you want to be lenient), you release the rest. Four hours become a few minutes — without control leaving the house.
That is the difference between «software you have to operate» and «an assistant that does the legwork while you keep your head».
Why «people decide» isn’t just nice to have — it’s necessary
In dunning, human approval is not a cosmetic touch; it is a must. A wrongly-sent second reminder to your most important customer is more expensive than ten reminders written by hand. Fully-automated «fire and forget» is the wrong model in customer contact.
So: the assistant does everything up to the last mile. The last mile — the judgement call — belongs to the human. That also lines up with what the four-eyes principle and the governance requirements of the EU AI Act suggest anyway: traceable, human-approved decisions instead of a black box.
What to watch for when you implement — even without us
Whether with an assistant, an ERP or Excel: these four points make the difference between defensible and shaky dunning.
- Document every stage verifiably. When was what sent? A gap-free reminder history is gold in a dispute.
- Calculate default interest correctly and consistently. 5 % under OR Art. 104, per day, 360-day basis — and the same method for every customer.
- Cover reminder fees contractually. A reminder fee without a basis in the contract or general terms is contestable.
- Separate routine from judgement. A system may prepare the standard case. The exception is decided by a human.
Conclusion
Default interest is not your problem — the lost time and the tied-up liquidity are. A good dunning process doesn’t bring in CHF 66 of interest, it brings in CHF 8’000 sooner, and gives you back the 50 hours per year that the manual dunning run eats up.
The 2026 question is therefore not «Which dunning module do I buy?», but «How much of this process can be prepared so my people only have to decide?».
hegyon.ai is an operational AI assistant for Swiss SMEs — with integrated modules for ERP, HR, CRM, ticketing, inventory, project management and wiki. The assistant prepares the work; your people decide. Swiss hosting, FADP/revDSG compliant, EU AI Act guardrails.