Interest calculated the way the law defines it

The aging shows where the exposure is, the reminder ladder works it, and where interest is due ComOps computes it the way the law defines it and issues it as a document of its own. This page follows a receivable from the day it falls due to the day it is settled, written off or time-barred.

Aging first, then allocation

Outstanding customer balances are bucketed by age, 0 to 30, 31 to 60, 61 to 90 and over 90 days, with the same treatment on the supplier side and on credit balances. A payment is allocated against invoices rather than swallowed whole: an allocation is written only if it fits both what is left of the payment and what is left of the invoice, so neither side can be over-allocated, and the invoice moves to partly paid or paid from that arithmetic rather than from a status somebody sets by hand. Bank statements arrive as CSV, are matched against open invoices with candidate suggestions you accept or ignore, and a batch pass clears the obvious ones in one go.

A reminder ladder you shape

Each step of the ladder says how many days past due it fires, whether it sends a reminder or a formal demand, whether the statement of account travels with it, and whether it puts the account on credit hold. A daily pass picks the highest step an overdue invoice has crossed and not yet been sent, once per step per invoice, so nobody is chased twice for the same thing. A reminder goes out as a numbered letter listing the open invoices and the interest accrued to date, filed against the customer with the date it left. A demand letter names each debt, the statutory rate and the article it comes from, the interest to date, the fixed compensation, the grace period you allow and what follows if it passes, over your bank details and signature.

Per customer, and per dispute

Per customer you set the billing address the letters go to, suspend the letters with a reason and an end date, and choose whether interest follows the statutory rate, a rate agreed in the contract, or nothing at all. Marking an invoice disputed stops the letters for that invoice while the interest keeps accruing, so settling the dispute does not cost you the interest. A ladder step can put the customer on hold or block them outright, so collecting the debt and deciding the credit are one process.

How the interest is actually calculated

The calculation runs in segments. A new segment begins wherever the principal or the rate changes; each segment is the principal times the annual rate, divided by the day-count basis, times the days it ran; and the total is the sum of the segments, rounded once at the end. Interest is not compounded. The Bulgarian pack and the neutral EU pack both count on a 360-day basis. Partial payments are events with a date and an amount, so the principal walks down over time, and if the balance reaches zero the accrual skips that stretch and picks up again if the balance rises. The rate comes from an effective-dated table: Bulgarian rows seeded half-yearly since 2015 citing decree ПМС 426/2014 as amended, and ПМС 347/2025 from 2026, alongside EU rows on the reference rate plus eight percentage points under Directive 2011/7/EU. When a decree changes the rate, the row is added in the app; nothing is edited in code.

An interest note is a document, with guards

An interest note is issued, numbered and filed like any other document, on its own numbering series that is never shared with invoices, credit notes or debit notes. The source invoices are locked before anything is read, and accrual continues from the day after the last day already billed, so a day is never charged twice. A unique key in the database holds the fixed compensation to once per invoice. Cancelling a note is refused across a closed period, refused when a later note has already billed past this one's last day, refused when a payment is allocated to it, and refused on the wrong status or document type. Interest and compensation sit outside the VAT base under the VAT Act (ЗДДС) art. 26(2), and the software refuses to issue a note that carries VAT or a line on any tax class but out of scope. How that tax class is decided is on the VAT engine page.

Fixed compensation, and the check behind it

Beyond the interest, a business debtor owes a flat EUR 40 per invoice towards the cost of collection, under the Commerce Act (ТЗ) art. 309а(1) as amended, and the neutral EU pack applies the same figure under Directive 2011/7/EU. Individuals are excluded, and the reason is recorded on the note. The legal basis is stored on the line and printed on the document. A check that runs over the whole database asserts four things about every interest note: that it carries no VAT and no line off the out-of-scope tax class, that its gross equals the sum of its accrual segments, that every source reference points at a live invoice or debit note belonging to the same customer and that no note is empty, and that at most one live compensation lock exists per source invoice. The calculation itself is pinned by tests covering segment splitting on a rate change, principal splitting on a partial payment, the zero and negative day boundaries, time-zone normalisation of the as-of date, the 365-day variant, rounding applied once, and a missing rate refusing rather than guessing.

The collections screen, and the end of a debt

The receivables screen shows the aging by customer, opens from any figure into the documents behind it, and carries the actions in one place: send a reminder, issue a demand, raise an interest note, send a statement, mark a dispute, place a credit hold. A statement of account covers any period you pick, with the opening balance, every invoice, credit note, payment and interest note in date order, the closing balance and the aging split. Every receivable also carries its limitation clock: the period runs from the due date, restarts on a part payment, an acknowledged statement or a filed claim, and the list flags what is close to time-barred while you can still act on it. Writing a debt off is a checklist against the grounds the law recognises, and it produces the document those grounds require, a credit note or a protocol, with the corporate-tax marker set and the status recorded on the invoice.

ComOps computes the amounts from the rules as configured and prints the article they rest on. Whether to charge interest to a particular customer stays a decision for the company and its accountant.

Questions we get asked

Which interest rate does it use?

The statutory rate in force on each day of the overdue period, from a table seeded with the Bulgarian decrees and the EU reference rate, and edited in the app when a new decree lands.

Is an interest note subject to VAT?

No. Interest and compensation fall outside the VAT base under the VAT Act (ЗДДС) art. 26(2), and ComOps refuses to issue an interest note that carries VAT.