If your Polish entity went live on KSeF and you expected faster collections, the numbers probably disappointed you. Invoices go out cleaner and faster, paperwork shrank, and payments arrive exactly as late as before. That is not a botched rollout. KSeF payment terms still come from your contract or from the Polish Act on Counteracting Excessive Delays in Commercial Transactions, not from the tax authority's platform.
Something else did change, and it is concrete. The issue date and the delivery date of every invoice now sit in a central state registry that neither party can dispute. The "we never received your invoice" defence is gone. Below: which dates actually drive your payment clock, the statutory ceilings on payment terms, what you are owed when a client is late, and what changes on 1 January 2027.
The three dates that drive your cash flow
One KSeF invoice carries several dates. Only some of them have legal weight.
Date Where it comes from What it governs Date in field P_1 Entered by the issuer in the XML file A mandatory invoice element, but in online mode it yields to the submission date Date of submission to KSeF The moment the file is sent Issue date (Art. 106na(1) of the Polish VAT Act) Date the KSeF number is assigned Assigned by the system Date the buyer is deemed to receive the invoice (Art. 106na(3)) Payment due date Contract or invoice The moment the claim falls due and interest starts running
The Ministry of Finance states this plainly: a structured invoice is deemed issued on the day it is submitted to KSeF and deemed received on the day the system assigns its identifying number (MF Eureka database).
The practical consequence: backdating is over. Submit the file on 3 March and you issued the invoice on 3 March, even if P_1 says 28 February. Every day you sit on a finished invoice is a day you push your own payment clock forward.
One exception. In offline24 mode the issue date is the P_1 date, and the file must reach KSeF promptly, no later than the next business day.
Mini-case: where the cash actually leaks
Service completed 20 March 2026. Invoice prepared 31 March, submitted to KSeF at 23:50 on 31 March, KSeF number assigned at 00:03 on 1 April. Payment terms: 30 days, so 30 April. The client pays on 12 May.
What happens in between:
The VAT point arose in March, when the service was performed (Art. 19a(1) of the VAT Act), not when payment lands.
You report that VAT in the March JPK_V7 file and pay it by 25 April.
The client's money arrives on 12 May.
For 17 days you finance the state budget out of your own working capital, on an invoice nobody has paid. That is the real cost of payment gridlock, and it never shows up in your P&L.
How long you can legally be made to wait
The Act on Counteracting Excessive Delays in Commercial Transactions sets hard ceilings (summary on biznes.gov.pl):
60 days between comparable private businesses. A longer term is valid only if the parties expressly agreed it, the creditor is not a micro, small or medium enterprise, and the arrangement is not grossly unfair to the creditor.
30 days where the debtor is a public entity.
60 days where the debtor is a public healthcare entity.
If you are an SME selling to a large Polish corporate, 60 days is a hard ceiling. A 90-day clause in that relationship does not bind you.
Where the parties agreed no term at all, interest starts after 60 days (private debtor or public healthcare entity) or 30 days (other public entities), counted from the day you performed.
What you are owed when a client pays late
Statutory late payment interest in commercial transactions accrues without any demand, by the fact of delay alone. From 1 July to 31 December 2026 the rate is 13.75% per annum, or 11.75% where the debtor is a public healthcare entity (announcement of the Minister of Finance and Economy, M.P. 2026 item 642).
On top of that sits a flat recovery-cost compensation, again with no demand needed and no obligation to prove actual costs:
the PLN equivalent of EUR 40 where the claim does not exceed PLN 5,000,
EUR 70 where it exceeds PLN 5,000 but is below PLN 50,000,
EUR 100 where it is PLN 50,000 or more.
Back to the example. On a PLN 12,300 gross invoice paid 12 days late, interest comes to roughly PLN 56, while the EUR 70 compensation is several times that. On small invoices the compensation, not the interest, is the real deterrent.
The third tool is VAT bad debt relief. If the receivable is neither paid nor assigned within 90 days of the due date, it is treated as probably irrecoverable and you may reduce your taxable base and output VAT (Art. 89a of the VAT Act). Art. 89b works symmetrically on the other side: a debtor who deducted the input VAT and did not pay must reverse that deduction for the period in which the 90th day fell, whether or not you claim the relief.
I am a software founder, not a tax adviser. The formal conditions in Art. 89a(2) are strict, so run the actual filing past your Polish accountant.
The trap: KSeF notifies nobody
This is where expectations and reality diverge most often. An invoice submitted to KSeF is legally delivered to the buyer, yet the buyer receives no signal at all. The official KSeF 2.0 handbook states that the system does not automatically send notifications about new incoming invoices. The Ministry's reasoning is that for taxpayers receiving high invoice volumes, per-invoice alerts would be a burden rather than a help.
So: legally your client has the invoice. Practically they may not know it exists for weeks if they log into KSeF once a month.
Two operational conclusions:
Keep emailing the invoice. A PDF, or just the KSeF number in the message body. It is not a legal requirement, it is liquidity management.
Pull your purchase invoices automatically. Otherwise you miss your own due dates and you miss errors on invoices someone issued against your NIP (Polish tax ID).
There is an exception for buyers covered by Art. 106gb(4) of the VAT Act, including entities without a seat in Poland. Those you supply outside KSeF in an agreed way, and the receipt date is the date of actual receipt. If your group has foreign affiliates buying from the Polish entity, this is the clause that applies to them.
From 1 January 2027: the KSeF number goes in the transfer title
Art. 108g of the VAT Act introduces a duty on the buyer from 1 January 2027. An active VAT taxpayer paying by bank transfer or direct debit for a structured invoice issued by another active VAT taxpayer must state that invoice's KSeF number in the transfer title, or a collective identifier where one payment settles several invoices. It also covers the split payment message.
Cash, card and BLIK payments fall outside the duty, as do situations where the seller is VAT-exempt. The buyer must also verify the seller's VAT status on the payment date against the official taxpayer list (Art. 96b of the VAT Act).
For cash flow this is good news. A transfer carrying the KSeF number is a transfer nobody has to reconcile by hand, which removes the single most common cause of "invoice still open despite being paid". Nothing stops you from putting KSeF numbers in transfer titles during 2026 and building the habit early.
One frequent misunderstanding: the KSeF number is not your invoice number. You assign the invoice number, the system assigns the KSeF number, and from 2027 both run in parallel.
Checklist: shorten your real time to cash
Submit to KSeF the day you finish the work. Submission date is issue date, so every day of delay is another day of free credit for your client.
Cut your default payment term. If 30 days is your standard, test whether 14 actually costs you customers. It usually does not.
Track DSO, not invoice count. Average days from issue to payment tells you whether the problem is one client or your own process.
Notify the client outside KSeF. An email with the KSeF number on submission day.
React the day after the due date, not a month later. Interest and compensation accrue automatically, so the first reminder can be short and polite.
Diary the 90th day after each due date. That is your bad debt relief decision point.
Use advance invoices on large engagements. They move part of the inflow to the start of the project instead of the end.
Conclusion
KSeF does not shorten payment terms. What it does is strip away the debtor's excuses and give you a state-certified delivery date for every invoice. The rest depends on how fast you issue, how short your terms are, and whether you actually know how long you wait for money.
Biurko puts that on one screen: payment status for every invoice (paid, unpaid, overdue), the total value of overdue receivables, and the average number of days from issue to payment. The KSeF number is stored on the invoice, ready for transfer titles before the 2027 duty bites. Create a free account at biurko.io and check your DSO against your own invoices.
FAQ
Does KSeF change invoice payment terms in Poland? No. Payment terms come from your contract or from the Act on Counteracting Excessive Delays in Commercial Transactions. KSeF only fixes the issue date (submission to the system) and the date the buyer is deemed to receive the invoice (assignment of the KSeF number).
When does a payment count as late under Polish law? From the day after the due date stated in the contract or on the invoice. From that day statutory late payment interest in commercial transactions accrues automatically, with no need to send a demand first.
What is the late payment interest rate in Poland in 2026? From 1 July to 31 December 2026 it is 13.75% per annum, or 11.75% where the debtor is a public healthcare entity. The rate is set for each half-year and published in a ministerial announcement.
Does my client get notified about a KSeF invoice? No. KSeF sends no automatic notifications about new invoices. The buyer has to check the system or use software that pulls invoices automatically, which is why emailing the invoice is still worth doing.
When can I recover VAT on an unpaid invoice in Poland? Once 90 days have passed from the due date without payment or assignment of the receivable. The debt is then treated as probably irrecoverable and you may correct your taxable base and output VAT under Art. 89a of the VAT Act, subject to the formal conditions.