The invoice as a primary accounting document: what the law actually requires

Why the invoice counts as a primary accounting document

An invoice is a primary accounting document, a piece of paper or a file that proves a business transaction happened between two parties: a sale of goods or a service. Two laws govern it at once. The Accounting Act sets the general requirements every primary document must meet (date, parties, subject, value), while the VAT Act (in Bulgarian, ЗДДС) layers on invoice-specific rules: an exact list of mandatory elements, issuance deadlines, and numbering.

• VAT (value added tax, ДДС in Bulgarian) is an indirect tax built into the price of almost every good and service. Companies registered for VAT charge it to their customers and remit it to the state through the National Revenue Agency (in Bulgarian, НАП), Bulgaria's tax authority.
• The invoice is the document that makes that charge visible: it shows how much of the price is the tax base and how much is the tax itself.
• This post is part of a series on primary accounting documents. It does not walk through issuing an invoice in a particular piece of software, we already cover that in a separate post, it explains what the law requires of the document itself, regardless of what tool produced it.

Getting this right matters in practice: an invoice missing a mandatory element can be challenged in a tax audit, and losing a VAT credit over one wrong field is an expensive mistake.

The mandatory elements under Article 114 of the VAT Act

There is no official invoice template in Bulgaria, but Article 114 of ЗДДС lists exactly what a document needs to contain to be valid. The list is long, but it groups into a handful of categories.

• The document title, the word "Invoice" (Фактура), and a sequential ten-digit number made up only of Arabic numerals, with no gaps and no repeats. A company with several outlets or lines of business can run several separate numbering series, but each series must stay unbroken.
• The date the invoice is issued, and, when the underlying supply (the taxable event) happened on a different date, that date too.
• The supplier's name, address, and company registration number (ЕИК), plus a VAT identification number if the supplier is VAT-registered.
• The same details for the buyer: name, address, and an identifier, a company number for a business or a personal ID number for an individual, plus a VAT number if the buyer is registered too.
• The quantity and type of goods, or the scope and type of service, described specifically enough that what was sold is unambiguous.
• The unit price excluding tax, and the tax base, the total value of the supply before VAT.
• The VAT rate (usually 20 percent, with reduced rates for specific services) and the VAT amount stated in euro, Bulgaria's official currency.
• The total amount due, VAT included.

Contrary to a common assumption, a company stamp, a signature, and spelling out the total in words are not legal requirements, even though many companies add them out of habit or internal policy.

Tax invoice vs. simplified invoice: the practical difference

The old version of ЗДДС formally split invoices into two categories, "tax invoice" (данъчна фактура) and "simplified invoice" (опростена фактура), but later amendments removed that formal split from the law. In everyday use, though, accountants and business owners kept both terms, because they describe a real difference in what the document contains.

• A "tax invoice" usually means one issued by a VAT-registered supplier: it shows the tax base, the VAT rate, and the VAT amount as separate line items, exactly as Article 114 requires.
• A "simplified invoice", or invoice without VAT, is one issued by a supplier who is not VAT-registered, often because their turnover sits below the mandatory registration threshold. No VAT is charged: the tax base equals the total due, because there is nothing to add on top.
• Both are fully valid invoices in the eyes of the law, as long as they carry the other mandatory elements. The difference lies only in the issuer's VAT status, not in the document's legal weight.

Do not confuse an invoice with a fiscal receipt (касова бележка). A fiscal receipt prints automatically from a cash register at the point of a cash or card payment, it proves the payment happened, but carries no buyer details and cannot support a deductible expense or a VAT credit claim. An invoice, by contrast, names both parties explicitly and is required whenever the buyer is a business or wants to claim the expense.

Issuance deadlines, numbering, and e-invoices

ЗДДС sets precise deadlines for issuing an invoice, and missing them is one of the most common findings in a Bulgarian tax audit.

• The general rule under Article 113(4) of ЗДДС: the invoice must be issued no later than 5 days from the taxable event, usually the date of delivery, or from the date an advance payment is received, if payment comes before delivery.
• For an intra-community supply of goods within the EU, the deadline is different: the invoice must be issued no later than the 15th day of the month following the month of the taxable event.
• Numbering must stay unbroken and free of repeats within each series in use. A gap in the sequence or a duplicated number is exactly the kind of red flag an auditor looks for as evidence of sloppy record-keeping.
• Electronic invoices carry the same legal weight as paper ones, as long as the authenticity of origin and the integrity of content are guaranteed, for example through a qualified electronic signature, EDI (electronic data interchange), or an internal control process that creates a reliable audit trail. The recipient also has to agree to receiving invoices electronically.

The practical takeaway: five days is a short window if you are waiting to collect paperwork from several staff members or locations, so issuing the invoice at the time of delivery, rather than batching it at month end, saves a lot of stress later.

How long to keep invoices, and how they differ from a protocol or a note

An invoice's life does not end on the day it is issued. The Accounting Act requires companies to keep accounting documents, invoices included, for 10 years, counted from 1 January of the year following the one they relate to, precisely because НАП can request access to them in a later audit or inspection.

• Protocol (протокол): a document distinct from an invoice, issued in specific cases where the supply itself is not documented with an invoice, for example an intra-community acquisition under reverse charge, a supply from an individual who is not VAT-registered, or certain self-charge cases under Article 117 of ЗДДС.
• Credit and debit notes (кредитно and дебитно известие): documents that correct an already-issued invoice, they do not stand in for a new transaction. A credit note reduces the tax base or the amount due (for a return or a discount, for example), a debit note increases it (for extra goods delivered later, for example). Both must reference the number and date of the invoice they correct.
• Neither a protocol nor a note can substitute for an invoice where the law specifically requires one, each has its own distinct role in the books.

Keeping the three straight avoids confusion at bookkeeping time: each document answers a different question, who supplied the goods or service, who corrected an invoice already issued, and who documented a transaction without a standard invoice.

The invoice is just the first document in the series

The invoice is the most recognizable primary accounting document a small company deals with, but far from the only one. Expense documents, tax filings, and correction notes each follow their own rules, worth knowing before you run into them in practice.

Useful next reads:

How invoicing will work with FreeMe.bg
Which expenses ЗКПО recognizes and how to document them
How VAT and tax filing will work with FreeMe.bg
How to issue an invoice: a step-by-step guide

FreeMe.bg keeps every invoice you issue and receive in one place, with automatic numbering and no risk of a missing field. Log in with your Google account and get your books in order without spreadsheets.