Tax audit or books investigation: what to expect and how to prepare
Written by Ilias Aarrass8 min read · Published on · Last reviewed on 
In short
A books investigation is always announced in advance and checks whether your returns match your records; cooperating and granting access is a statutory duty.
- If your records fall short or you do not cooperate, the burden of proof can be reversed: you then have to show the inspector's estimate is too high.
- You must give access to the premises where your business is located and to your records, and allow copies to be made.
- If you find an error yourself, report or correct it proactively; that counts in the assessment and can limit a penalty.
- You can object within six weeks to any additional assessments that follow from the investigation.
Most freelancers never experience one, but it can happen to anyone: a books investigation. The tax authorities then check whether your returns match your records. If your affairs are in order, there is nothing to fear, but it helps enormously to know how such an investigation works and what is expected of you. This article walks through the process step by step: the forms it takes, what the inspector looks at, what your rights and obligations are and how to prepare.
How a books investigation starts
A books investigation is almost always announced in writing or by phone. The announcement states which taxes are being checked, for example VAT or income tax, which years are covered, and whether it concerns your entire return or specific elements such as mileage records or input VAT. Sometimes it stays limited to a request to send in documents; sometimes the auditor visits your business address or your bookkeeper. The trigger can be anything: striking fluctuations in your figures, a sector receiving extra attention, a tip-off, or simply a random sample.
Not every check is equally heavy. It saves a lot of tension if you know which form you are dealing with.
| Form | What it involves |
|---|---|
| Letter of enquiry | A written question about a single item in your return. No visit, but a response deadline |
| Partial investigation | A check on one element, for example input VAT or time records |
| Full books investigation | The entire administration over one or more years, usually with a visit |
| On-site observation | An unannounced visit to see how you work, mainly in cash-heavy sectors |
What the inspector looks at
The core of every investigation: do your records match your returns, and are the records themselves reliable? Concretely, the auditor looks at the completeness of your revenue (invoices, bank statements, cash records), the business nature of your costs (invoices and receipts, mixed costs, private use), the VAT (correct rates, rightly claimed input tax, reverse-charge schemes) and specific deductions such as the self-employed deduction, for which your time records are the evidence.
In sectors with a lot of cash, the emphasis is on cash records and the match between diary, till and bank. For service providers, it is more often about time records, the business nature of costs and VAT on foreign transactions.
- Completeness of your revenue: do your invoices, bank statements and cash records reconcile?
- The business nature of your costs: can every item be traced to an invoice, and is the split correct for mixed costs? See which costs are deductible.
- VAT: the correct rates, rightly claimed input tax and the reverse-charge schemes.
- The self-employed deduction, for which your time records are the only evidence.
- Private use of car, phone and workspace, and whether the mileage log adds up.
Your obligations: cooperate and retain
As an entrepreneur you have a statutory duty to provide information: you must supply the data and details that may be relevant to your taxation, and give the auditor access to your records. Those records must be kept for seven years, ten for immovable property. If your records fall short, or you refuse to cooperate, the tax authorities can reverse and increase the burden of proof: the inspector then makes a reasonable estimate and you must convincingly demonstrate it is too high. You want to avoid that position at all costs. Often that request first arrives by letter; see answering a questions letter.
In return, the auditor must show identification before starting, may only enter your private home with your consent, and records the findings in an audit report. In practice those findings are discussed in a closing meeting, so you can respond before any assessments follow. The retention period and the requirements for your records are in record retention.
How to prepare
Read the announcement carefully: which tax, which years, which elements. Have the requested documents complete and organised: invoices, bank statements, cash book, contracts, time records and mileage logs. Critically review the years in question yourself in advance, or have your bookkeeper do so. If you find an error yourself, it is often wise to report or correct it proactively via a supplementary return; that counts in the assessment and can limit a penalty.
Have your bookkeeper or adviser assist you during the investigation. Answer questions factually and completely, but do not speculate or guess: 'I will look that up and get back to you' is a perfectly good answer. Take your own notes of what was discussed and which documents were handed over.
- Read the announcement and note exactly which tax, which years and which elements are covered.
- Prepare the requested documents per year in one folder: invoices, bank statements, cash book, contracts, time records and mileage logs.
- Check the reconciliation yourself: turnover per your invoices against your bank transactions, and your VAT returns against your ledger.
- If you find an error, correct it proactively, for example via a supplementary return. That counts in your favour and can limit a penalty.
- Agree that questions go through your bookkeeper, so you do not have to answer from memory on the spot.
What you had better not do
Editing or supplementing documents after the fact is the worst thing you can do: it shows, and it turns a discussion about figures into a discussion about your reliability. Records assembled over the weekend before the visit also stand out. If something is missing, just say so. A gap you name yourself weighs less than a gap the inspector finds. If you are behind on your bookkeeping, read clearing a backlog.
And afterwards?
Afterwards you receive the audit report. If everything is approved, you are done and you also know your records pass the test. If there are corrections, additional assessments follow, possibly with tax interest and a penalty where there is culpability. You can object to those assessments within six weeks. The best insurance against all of this remains an administration that is maintained continuously rather than reconstructed afterwards: then a books investigation is mostly a formality.
If you cannot pay an additional assessment in one go, do not wait: payment arrangements exist, but you have to ask for them. See unable to pay your tax.
Frequently asked questions
How often does a books investigation happen to freelancers?
Rarely. Most freelancers never experience one. The chance is higher in cash-heavy sectors, with striking fluctuations in your figures or after a tip-off. Random samples exist too.
Must I give the auditor access to my accounting software?
You must give access to your records in a form that can be checked. Often an export of your ledger and journal entries suffices; full access to your account is not required. Discuss this with your bookkeeper.
Do I automatically get a penalty if something turns out to be wrong?
No. A correction leads to an additional assessment with tax interest. A penalty only comes into play with culpability, such as gross negligence or intent. A mistake you can explain usually does not qualify.
Can I postpone a books investigation?
Rescheduling an appointment is usually possible, for example due to illness or holiday. Refusing the investigation is not: cooperating is a statutory duty. Ask for a postponement with a reason and a new date.
What if I disagree with the audit report?
In the closing meeting you can respond to the findings before any assessments follow. If you still disagree, you file an objection within six weeks of the assessment. Get assistance, because the substantiation is what counts.
Sources
- What happens during a books investigation or visitBelastingdienst · belastingdienst.nl
- Rules during an inspection: rights and obligationsBelastingdienst · belastingdienst.nl
Sources checked on
This article provides general information based on the rules known for 2026 and does not replace personal tax advice. For your specific situation, we're happy to take a look with you.
