What are the Different Types of Invoices? Issuance, Storage, and 2026 Rules.

What is an invoice?

An invoice is an official document that records a commercial transaction between a seller and a buyer, showing the amount owed by the customer for goods sold or services rendered. It is not merely proof of payment, but also legal proof of the transaction between the parties: it proves that goods were sold or services were provided, the price was paid, and the buyer-seller relationship exists.

Invoices serve three essential functions for businesses:

• Proof of the debtor-creditor relationship: Clearly documented who owes whom how much.
• The basis for tax obligations: Expenses can only be recorded as deductible expenses and VAT deductions applied with an invoice; expenses without invoices are, in most cases, non-deductible from the tax base.
• Record keeping: This is the fundamental basis of accounting records and declarations.

For individual customers, the invoice is important as proof of ownership of the purchased product, for exercising warranty/return rights, and as evidence in potential disputes.

What is the difference between an invoice and a receipt?

Although both invoices and receipts document a sale, their legal status differs.

The threshold for distinguishing between receipts and invoices is updated annually according to the revaluation rate and announced by the Revenue Administration (GİB) via a circular; therefore, it is necessary to check the current amount every year.

What are the different types of invoices?

Invoices are not a single, uniform document; they are categorized into different types depending on the nature of the transaction, the method of taxation, the payment status, and the method of delivery.

1. Invoice Types According to Transaction Purpose

• Sales invoice: A standard type of invoice issued for the sale of goods or services.
• Return invoice: Issued by the buyer to the seller when a purchased item is returned; it corrects the previous sales invoice in the accounting records through a reverse transaction.
• Proforma invoice: A preliminary information document, without monetary value and not recorded in accounting, provided to inform customers of price and delivery terms before a sale.
• Delivery note invoice: This type of invoice combines a delivery note and an invoice into a single document, showing both the shipment of goods and the sale.

2. Invoice Types According to Taxation Method

• Withholding tax invoice: Instead of the entire VAT being paid by the seller, it is declared by sharing the amount between the buyer and seller according to a predetermined ratio. This is generally applied in public institutions and certain sectors.
• Withholding tax invoice: This type of invoice shows that the income tax withheld is deducted by the payer and paid to the tax office; it is common in freelance businesses.
• Invoices including Special Consumption Tax/Special Communication Tax: These are invoices that include Special Consumption Tax or Special Communication Tax in addition to VAT in areas such as fuel, tobacco, alcoholic beverages, and communication services.

3. Invoice Types According to Payment Status

• Open invoice: Issued when the sales price has not yet been collected; commonly used for sales on credit.
• Closed invoice: Issued when the sales price is collected in cash; frequently used for payments made in cash or by credit card.

4. Invoice Types According to Delivery Method

• Paper invoice: A traditional invoice that is physically printed and delivered; used by businesses that are not subject to e-Invoice/e-Archive regulations.
• e-Invoice: If both parties are subject to e-invoicing, the invoice is issued digitally through the GIB (General Directorate of Taxation) system.
• e-Archive invoice: Issued if the recipient is not an e-invoice taxpayer (e.g., a final consumer), and sent via email or SMS.
• e-Export invoice: A type of digital invoice issued for sales made abroad and used in customs procedures.
• e-Freelance Professional Receipt (e-FPR): An electronic document issued by freelance professionals (lawyers, financial advisors, doctors, etc.) in exchange for their services.

Mandatory Information That Must Be Included on the Invoice

For an invoice to be considered valid, it must contain the following information in full:

• Invoice date, serial number and sequence number
• Seller's name/title, address, tax office and tax identification number/national identification number information.
• Recipient's name/title, address and tax identification number/national identification number information.
• Type, quantity, and unit price of the goods/services sold.
• Cost of goods (taxable base), VAT amount and other taxes, if any.
• Total invoice amount

The invoice may be considered invalid if any of this information is missing or incorrect.

Invoice Issuance Period: 7-Day Rule

The invoice must be issued within seven days of the date the goods are delivered or the service is completed. The delivery/completion day is not counted when calculating the time; the count begins the following day. Invoices not issued within this period will be considered as never having been issued and may be deemed irregular.

How many copies of the invoice should be issued?

Invoices are prepared in at least one original and one copy. For delivery invoices, at least three copies are prepared: the first copy goes to the customer, the second to the accounting records, and the third to the company archives. Printing the copies in different colors is common practice to avoid confusion.

How to cancel an incorrect invoice?

Erasures, alterations, or corrections cannot be made on incorrectly issued invoices. The correct method is to draw a double line through the original invoice and all copies, write "Cancelled," and keep it in the invoice archive in this state. Cancelled invoices are not thrown away.

How and for how long should invoices be kept?

Invoices must be kept for five years according to tax regulations. For paper invoices, keeping the original copy is essential; if it is lost, the tax office must be notified. For e-invoices, there is no obligation to print them; the documents are archived electronically. For e-archive invoices, the document must be downloaded electronically from the e-document portal or printed and kept.

What is a fake (nylon) invoice?

A fictitious invoice is a document that appears to be a normal invoice but is fake or misleading, issued for a good or service that does not actually exist. It is often used to inflate expenses and pay less tax, and those who issue or use them face serious penalties, including heavy fines and imprisonment. Suspicious invoices should always be discussed with a financial advisor before being recorded.

Things to Consider in Billing Processes in 2026

The Turkish Revenue Administration is gradually expanding the scope of e-Invoice and e-Archive Invoice applications over the years: the transition to e-Invoice, which was previously mandatory for businesses exceeding a certain turnover threshold, has grown to include smaller businesses as well. By 2026, the general trend is for the use of paper invoices to become increasingly exceptional and for digital invoicing to become the norm.

Since these limits and scope are subject to annual updates, we recommend that you confirm your business's current e-Invoice/e-Archive obligation status with your local tax office or financial advisor. Businesses that have not yet switched to a digital invoicing system should prepare their processes in advance to ensure timely compliance with any potential new requirements.

Risks of Tracking Paper/Manual Invoices

Businesses that still rely on paper invoices or manual Excel tracking face the following risks:

• Losing invoices or taking time to archive
• The seven-day adjustment period was overlooked during manual tracking.
• The inability to properly differentiate between different invoice types (e-invoice/e-archive/paper invoice)
• Errors resulting from manual calculation of VAT and other taxes.
• Invoices that are not integrated with the accounting program are processed late or incorrectly into the current account.

Digitize your billing processes with FlatERP.

FlatERP's e-Transformation module minimizes time and cost losses by digitizing your invoices using e-Invoice, e-Archive, e-Delivery Note, and e-Ledger systems. Determining the correct invoice type based on the recipient's tax status reduces the risk of manual errors.

With FlatERP's Pre-Accounting module, every invoice you issue is automatically processed into the customer's account; the customer balance, average due date, and late payment periods are calculated by the system, and automatic payment reminders are sent to your debtor customers.

With the finance module, you can track your cash flow related to your invoices, and your daily collections and payments, all from a single screen.

Thanks to FlatERP's web-based infrastructure, you can manage your billing processes from anywhere using a PC, tablet, or mobile device.

Try FlatERP for free today to digitize your billing processes.

Frequently Asked Questions

Why is an invoice required? An invoice provides official documentation of a purchase or service; for businesses, it allows for expense deduction and VAT reduction, while for individual consumers, it provides proof of ownership and guarantee/return rights.

Are invoices and receipts the same thing? No. Receipts are issued for retail and immediate sales without the buyer's information. Invoices, on the other hand, contain the buyer's information, are mandatory for B2B transactions, and provide expense/VAT deductions.

Within what is the maximum number of days required to issue an invoice? Within seven days of delivery of the goods or completion of the service. If this period is exceeded, the invoice will be considered never issued.

What is the difference between an open invoice and a closed invoice? An open invoice is issued when payment has not yet been collected (credit sale), while a closed invoice is issued when payment is collected in cash.

What is the difference between an e-invoice and an e-archive invoice? An e-invoice is issued only if the recipient is also an e-invoice taxpayer. An e-archive invoice is issued if the recipient is not an e-invoice taxpayer (for example, if they are an individual customer) and is sent via email/SMS.

Is a proforma invoice an official document? No. A proforma invoice is an informational document issued to inform customers of prices and terms before a sale; it is not recorded in accounting records.

What happens if the wrong invoice type is selected? The document may be deemed invalid, the right to deduct VAT or treat it as an expense may be lost, and penalties for irregularities may be incurred; therefore, it is important to correctly determine the taxpayer's status.

How does FlatERP simplify invoicing processes? FlatERP's e-Transformation module allows you to manage your e-Invoice, e-Archive, e-Delivery Note, and e-Ledger transactions from a single platform. The Pre-Accounting module automatically processes the invoices you issue to the customer account and sends payment reminders.