JPK_CIT for 2026 in an accounting office: the marker goes on the account, so the chart of accounts is the problem

The First Year That Counts Is Already Nine Months Old

For most of the full-books clients in a typical Polish accounting office, 2026 is the first year that ends up in JPK_CIT. The file itself isn't due until the annual return: 31 March 2027 for a CIT company on a calendar year, 30 April 2027 for a PIT taxpayer on full books. That deadline makes it feel like a spring problem.

It isn't. The data that goes into the file has been posted since January. Whatever shape your clients' charts of accounts are in today is the shape the 2026 file will have, unless someone fixes it while it's still cheap.

Quick recap of who files what. The Ministry of Finance rolls this out in three stages. Taxpayers with revenue above 50 million euro and tax capital groups started with 2025 (and their first deadline was pushed back to 31 July 2026). For tax years beginning after 31 December 2025, the rest of the CIT taxpayers obliged to file JPK_VAT join, along with PIT taxpayers who file JPK_VAT, each with the structure that matches their records: JPK_KR_PD for full books, JPK_PKPiR for the revenue and expense ledger, JPK_EWP for lump-sum tax, plus the fixed-asset registers. Everyone else follows a year later. For an accounting office, that means most of your active VAT payers on full books arrive in the same year: 2026.

This post is about JPK_KR_PD, because that's where the work is.

The Marker Goes on the Account, Not the Entry

JPK_KR_PD is the accounting ledger plus markers. Every account that has an opening balance or entries in the period gets markers from the dictionary in the MF regulation (Annex 7 to the regulation on additional data for accounting records): one set for the balance sheet, one for the profit and loss account, and tax markers marked "PD". The tax markers are the reason this file exists. They connect the books to the CIT calculation, so the tax office can see which costs you treated as deductible without asking for your spreadsheet.

The important word is account. You don't mark entries. You mark accounts, and every entry on that account inherits the marker.

That turns a reporting question into a chart-of-accounts question. If an account holds costs that are all treated the same way for tax, assigning a marker takes a minute. If it holds a mix, no marker is correct. You have to split the account. Do that in March 2027 and you're moving twelve months of entries.

Where the Mixed Accounts Hide

Every office has its own, but the same few show up in nearly every chart of accounts I've looked at:

• Representation and marketing on one account. Representation costs are non-deductible under the CIT Act (art. 16 sec. 1 point 28); advertising generally is. A single "reprezentacja i reklama" account is one of the most common setups in small companies.
• Car costs. Running costs of a passenger car used for both business and private purposes are deductible at 75% (art. 16 sec. 1 point 51). One "eksploatacja samochodów" account carrying a mixed-use car and a company-only van can't carry a single tax marker.
• Interest. Interest on a bank loan and interest on tax arrears land on the same "odsetki" account surprisingly often. One is deductible, the other isn't.
• Penalties and damages. Contractual penalties, fines and late-payment compensation mixed together on "pozostałe koszty operacyjne".
• FX differences. Realised and unrealised differences on one account, where the tax treatment depends on which is which.

Most offices have handled these until now with an Excel sheet at year-end: take the account balance, subtract the non-deductible part, done. The file doesn't allow that any more. The adjustment has to live in the books.

What It Costs Across a Portfolio

Some rough arithmetic. Take an office with 40 clients on full books. Say a typical client has 250 analytical accounts with movement this year. Assigning markers to the straightforward ones at about a minute each is four hours per client, or 160 hours across the portfolio. That's a month of one accountant's time before anyone has dealt with a single mixed account.

Then the mixed ones. If you split a mixed account in October, you set up two new analytical accounts, re-book nine months of entries (often a few dozen documents) and post the rest of the year correctly. If you split it in March, you do the same with twelve months, during the busiest weeks of the year, and you probably also have to re-check the CIT advance payments you calculated in between.

The rule I'd use: every mixed account found before December is a chart-of-accounts fix; every one found after January is a correction project.

Generate a Trial File Now

The single most useful thing to do in October is to generate a trial JPK_KR_PD for January to September for each client. Optima, enova365 and the other mainstream ERPs already support the structure; the Comarch help has had a page on markers in Optima since 2025. You won't send this file. You'll read it.

What the trial file tells you:

1. Accounts without markers. The ERP will either refuse to generate or produce gaps. This list is your workload, per client.
2. Entries without a counterparty NIP. The MF Q&A lists the counterparty identifier as optional but recommended. A high share of empty values usually means documents were booked from summaries rather than invoice by invoice.
3. Entries without a KSeF number. For operations documented with an invoice issued in KSeF, the MF Q&A says the KSeF number field is required. If your clients' purchase invoices are booked from PDFs and the KSeF number never reaches the ledger, 2026 is the year that shows. I covered how the number gets into the books in automatic KSeF downloads, and the same gap on the VAT side in JPK_V7 markers.
4. Accounts that look mixed. This one the ERP won't tell you. You find it by reading entry descriptions.

Points 1–3 are counting. Point 4 is reading. Both are tedious. Both get worse with every client you add.

One more thing from the MF Q&A that's better learned now than in March: the tax reconciliation section (RPD) is filled in only in the file that closes the reported period. Interim files carry zero there. So a trial file will look complete even though the hardest part of the reconciliation isn't in it yet.

What an Agent Does, and What Stays With the Accountant

This is nearly ideal work for an AI agent. Most of it is reading a lot of data and handing a person a short list.

The agent can:

• generate the January–September trial file for each client and keep a per-client status: generated, failed, gaps found;
• list accounts without markers and propose a marker from the account name, its history and the markers on similar accounts at other clients;
• read entry descriptions on each cost account and flag accounts where they cluster into groups with different tax treatment ("mandat", "kara umowna", "catering", "paliwo"). That turns "check every account" into "check these nine";
• measure the share of entries without a counterparty NIP and without a KSeF number, per client and per month, so you can see whether the gap is a habit or one bad month;
• compare the deductible and non-deductible totals implied by the proposed markers with the figures used for this year's CIT advances, and show where they disagree.

The accountant keeps:

• every decision about whether a cost is deductible. That's a tax judgement, and the agent's proposal is a starting point, not an answer;
• the decision to split an account and how to re-book it;
• the RPD reconciliation and the final file;
• the conversation with the client about what changed in their chart of accounts and why.

It's the same line I draw in every accounting project: the agent prepares, a person signs. I wrote about it in more detail in AI agents and liability, and about where the limits are for JPK files in JPK_V7 corrections and what an agent won't do.

A Calendar That Works

• October: list each client's stage. Generate trial files. Count accounts without markers and entries without NIP or KSeF numbers.
• November: fix the charts of accounts. Split mixed accounts, re-book this year's entries, assign markers. Do it alongside the balance confirmations, which run on the same settlements anyway.
• December: generate a second trial file for January–November. The marker gaps should be close to zero; whatever is left is a named list, not a surprise.
• January–March: close the year, fill in the RPD section, send.

The year-end close is already the most compressed period of the year, as I described in month-end close in an accounting office. JPK_CIT adds another job to it. Moving the chart-of-accounts work to October and November is the only lever that doesn't cost anything.

One Number to Start With

If you do one thing this month, generate a trial file for your three biggest full-books clients and count accounts with movement and no tax marker. Multiply by your client count and you have an honest estimate of the work before March.

If you'd like a second pair of eyes on that number, or you want to see what the reading part looks like when an agent does it, write to me. I'll go through one client's chart of accounts with you and tell you honestly whether automation is worth it at your scale.