i.SAF is not the same as sending an invoice to your client
i.SAF is a subsystem of the State Tax Inspectorate (VMI), Lithuania's tax authority, through which VAT payers submit register data for the VAT invoices they've issued and received. It sits inside i.MAS, VMI's smart tax administration system, specifically as the invoice-data module. i.SAF doesn't send an invoice to your client automatically: you still issue that invoice in your accounting software, in Excel, or by hand, and deliver it to the client the usual way. i.SAF only receives the summarized data afterwards. Legal entities submit this data for each calendar month by the 20th of the following month, which means the July 2026 register is due by 20 August 2026. Since 1 May 2025, this obligation no longer applies to VAT payers who apply the small business scheme in Lithuania. There's also a separate, narrower i.SAF function, the VMI e-invoice service, which we cover at the end of this article.
Who must submit i.SAF data in 2026?
Every taxable person who issues and/or receives VAT invoices has to keep registers, regardless of whether they're registered for VAT. But the obligation to actually submit that data to VMI falls only on those registered as VAT payers in the Republic of Lithuania. That distinction matters: issuing an invoice on its own does not trigger a submission duty. The exception is VAT payers who've chosen to apply the small business scheme (SBS) in Lithuania. Since 1 May 2025, they don't submit i.SAF data at all, neither for issued nor received invoices. This is where people mix things up with the €45,000 threshold: that figure decides who is eligible to choose SBS status, not whether a given company has to submit i.SAF data. What actually decides it is registration status, not turnover: a standard VAT payer submits data, an SBS participant does not.
Deadlines: why the 20th of the month matters for most companies
For legal entities, the tax period is the calendar month, and data is due by the 20th of the following month. For sole proprietors, the deadline depends on their assigned VAT reporting period: if it's monthly, the same 20th-of-the-next-month rule applies; if it's semi-annual, the deadline is the 20th of the first month of the following half-year. In practice that gives you one concrete number to remember: a legal entity closing out July has to submit that register by 20 August 2026. It's a fixed date, not "sometime before month-end, whenever's convenient."“
What belongs in the purchase and sales invoice registers?
The sales invoice register records invoices issued to buyers during the tax period for goods supplied and services rendered, along with credit notes, debit notes, and advance invoices. The purchase invoice register, correspondingly, records VAT invoices received from suppliers, plus any credit notes received. Since 1 May 2025, issued e-receipts also have to go into the sales register. That's relevant only to businesses that actually issue receipts of that kind. The practical rule: your registers need to show the same counterparties, amounts and dates that appear in your bookkeeping. i.SAF isn't a separate, parallel system: it has to match what your books already say.
How do you actually submit i.SAF: by hand, XML file, or integration?
There are three ways to get data into i.SAF: filling out the register manually directly in the system, uploading a prepared VAT invoice data file (XML, a standardized file format used to exchange structured data between systems), or using the i.SAF web service, which is what most accounting software relies on for automatic transfer. For a small business with, say, one €1,200 invoice a month, manual entry is genuinely the most practical route: the buyer's name, invoice number and date, taxable value, and VAT amount. And even if you had no invoices at all during a period, either received or issued, you still have to submit the register, just an empty one, or one noting there were no invoices.
Mistakes, corrections, and i.SAF cross-checking
If you spot your own mistake after submitting (a wrong amount, a missed invoice, an incorrect buyer code), you need to submit corrected data for the same tax period rather than wait for VMI to catch it. But if i.SAF flags a mismatch between your data and your counterparty's purely because the counterparty made the error, and your own register is correct, you don't need to touch your own figures. Worth knowing, so you don't end up rewriting your accounts over someone else's mistake. Check first which side's data actually disagrees with what's on the invoice.
When is the i.SAF e-invoice service actually worth using?
Alongside the general register-submission duty, i.SAF also runs a separate, narrower feature: an e-invoice issuing and receiving service. Only sole proprietors (individuals running individual activity) can issue invoices through it, while both sole proprietors and VAT-registered companies in Lithuania can receive them. One condition matters here: the invoice only reaches the recipient inside i.SAF if that recipient has already agreed in advance to receive e-invoices through i.SAF and can be found in the taxpayer register. Otherwise, the seller can only print the invoice and deliver it the ordinary way. So this service is only worth choosing when both sides of the transaction already use i.SAF and consent has been given; for everyone else, sending the invoice to the client and submitting the i.SAF register to VMI remain two completely separate steps.
FAQ
Do I have to submit i.SAF data in 2026?
All VAT registered persons in Lithuania who issue and/or receive VAT invoices must submit data to the i.SAF registers. The exception is VAT registered persons who implement the Small Enterprise Scheme (SVS) - they will not submit data to the i.SAF from 1 May 2025.
When is the deadline for submitting i.SAF data in 2026?
Legal entities submit data for the calendar month by the 20th of the following month. For example, registers for July 2026 must be submitted no later than August 20, 2026. For natural persons, the deadline depends on the period of their VAT return.
How to submit i.SAF data?
Data can be submitted in three ways: by manually filling out the register in the system, by uploading an XML file, or via the i.SAF web service, which is mostly used by accounting programs for automatic transmission. If there are no invoices during the period, an empty register must still be submitted.
What to do if an error is discovered in the data submitted to i.SAF?
If an error is discovered, corrected data for the same tax period must be submitted. If the discrepancy arises because the other party made the error, not you, then you do not need to correct your register - first check which party made the error.