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One-person business accounting step by step: what you need to do every month

Expert knowledge. Content verified: 7 November 2026.

In a one-person business the same deadlines come back every month: sales invoices by the 15th, entries in the ledger, ZUS contributions and the income tax advance by the 20th, and VAT by the 25th. Below are the steps in order, with the legal basis. Check the exact deadlines for your form of taxation and your VAT settlement method.

Step 1: issue invoices and collect documents

  • You issue a sales invoice no later than the 15th day of the month following the month of delivery of the goods or performance of the service (art. 106i para. 1 of the VAT Act). If you receive full or partial payment before the delivery or service, the deadline runs from the month in which payment was received (para. 2).
  • Collect the purchase invoices, receipts and other cost documents for the month. The right to deduct input VAT arises in the settlement for the period in which the seller's tax liability arose, no earlier than for the period in which you received the invoice (art. 86 para. 10 and 10b of the VAT Act).
  • If you do not deduct VAT in that period, you can do so in one of the next three settlement periods, or in one of the next two for quarterly settlement (art. 86 para. 11).
  • Match payments to invoices, for example based on a bank statement, so you know which receivables and payables are still open.

Step 2: post the documents

  • KPiR: you enter invoice revenue no later than the 20th day of the month following the month in which it was earned (§ 11 para. 2 of the regulation, Dz.U. 2025 poz. 1299). After the month ends you total the data from columns 9–16.
  • Revenue ledger under flat-rate tax: entries no later than the 20th day of each month for the previous month (§ 6 of the regulation, Dz.U. 2025 poz. 1294).
  • You enter expenses in the ledger according to the rules for deducting costs from the PIT Act (§ 10 of the KPiR regulation).
  • You correct an error in the KPiR in line with § 6 para. 2: you enter the new content of the entry or a correction with a minus sign.

Step 3: ZUS contributions

  • A payer who pays only contributions for their own insurance, and a business without legal personality, pays contributions and submits the ZUS DRA settlement return by the 20th day of the following month (ZUS information on deadlines).
  • The health contribution base on the tax scale and flat 19% tax is the income from the previous month, not less than 4 806 PLN in the contribution year from 1 February 2026 to 31 January 2027. Under flat-rate tax the base depends on cumulative revenue from the start of the year (the thresholds are described in the article on choosing between the KPiR and flat-rate tax).
  • If the deadline falls on a holiday, Saturday or Sunday, the last day is the next working day.

Step 4: income tax advance

  • Tax scale and flat 19% tax: monthly advance by the 20th day of the following month, for December by 20 January (art. 44 para. 6 of the PIT Act). Quarterly advances may be paid by, among others, small taxpayers and those starting a business (art. 44 para. 3g).
  • On the tax scale, the obligation to pay advances arises from the month in which cumulative income exceeds the quotient of the tax-reducing amount and the lowest rate, i.e. 30 000 PLN (art. 44 para. 3 point 1).
  • Flat-rate tax: tax for a month by the 20th day of the following month. It can be paid quarterly by those starting a business and by taxpayers whose revenue in the previous year did not exceed 200 000 euro (art. 21 para. 1, 1a and 1b of the Flat-Rate Tax Act).

Step 5: VAT for active taxpayers

  • Monthly settlement: JPK_V7M (records and return together) and payment of VAT by the 25th day of the following month (art. 99 para. 1 of the VAT Act).
  • Quarterly settlement available to small taxpayers (art. 99 para. 2 and 3): the return and tax by the 25th day of the month after the quarter, and you send the records part of JPK_V7K every month by the 25th day of the following month (biznes.gov.pl).
  • A deadline falling on a Saturday, Sunday or holiday moves to the nearest working day (biznes.gov.pl, art. 12 § 5 of the Tax Ordinance).

Step 6: close the month and keep the documents

Check that the entries in the ledger match the invoices and the bank statement, and correct errors as you go, because entries have their own deadlines. Tax books and related documents are kept until the limitation period of the tax liability expires (art. 86 § 1 of the Tax Ordinance). A liability is time-barred after 5 years, counted from the end of the calendar year in which the tax payment deadline passed (art. 70 § 1). Once a year there is the annual return, filed from 15 February to 30 April of the following year (art. 45 of the PIT Act, art. 21 para. 2 of the Flat-Rate Tax Act).

How it works in Zaksio

Anna and Kasia are software (an AI team), not an accounting firm or a tax adviser. Anna, the AI accountant, prepares proposals and you approve them: by default nothing is posted without your decision.

  • You download purchase invoices from KSeF after connecting your own token, or load them from a scan or photo. Anna proposes the posting with a justification, and the entry is created after approval.
  • Importing bank statements (MT940 and CSV) with payments matched to invoices helps complete the first step.
  • Entries in the KPiR or revenue register are created from invoices and purchases, and the obligations calendar shows the deadlines resulting from your tax profile, including VAT/JPK and advances.
  • Zaksio prepares a draft JPK_V7M or JPK_V7K and an XML file that conforms to the schema. Anna proposes preparing the draft herself after the period ends, once the tax profile is complete. You or your accounting firm download and file the file.
  • Amounts, VAT and advances are calculated by deterministic code, not an AI model. The Start plan is free within limits; you can find their size in the Zaksio price list.

Sources

  • Act of 11 March 2004 on Value Added Tax, consolidated text Dz.U. 2026 poz. 1263 (art. 86, 99, 106i) — https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU20040540535
  • Act of 26 July 1991 on Personal Income Tax, consolidated text Dz.U. 2026 poz. 592 (art. 44, 45) — https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19910800350
  • Act of 20 November 1998 on the Flat-Rate Income Tax on Certain Revenues Earned by Natural Persons, consolidated text Dz.U. 2025 poz. 843 (art. 21) — https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19981440930
  • Act of 29 August 1997, Tax Ordinance Act, consolidated text Dz.U. 2026 poz. 622 (art. 12, 70, 86) — https://isap.sejm.gov.pl/isap.nsf/DocDetails.xsp?id=WDU19971370926
  • Regulations of the Minister of Finance and Economy of 6 September 2025: on keeping the tax revenue and expense ledger (Dz.U. 2025 poz. 1299) and the revenue ledger and the register of fixed assets and intangible assets (Dz.U. 2025 poz. 1294) — https://www.gov.pl/web/finanse/publikacja-rozporzadzen-ministra-finansow-i-gospodarki-dotyczacych-ksiag-podatkowych
  • ZUS: Deadline for submitting documents and paying contributions — https://www.zus.pl/firmy/rozliczenia-z-zus/dokumenty-rozliczeniowe/termin-skladania-dokumentow-i-oplacania-skladek
  • ZUS: Information on the contribution base and the amount of the health insurance contribution in 2026 — https://www.zus.pl/-/informacja-w-sprawie-podstawy-wymiaru-sk%C5%82adki-oraz-kwoty-sk%C5%82adki-na-ubezpieczenie-zdrowotne-w-2026-r.
  • Biznes.gov.pl: How to settle VAT correctly — https://www.biznes.gov.pl/pl/portal/00232

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