How to change your provisional assessment mid-year
When your profit changes unexpectedly, adjust your provisional tax assessment to avoid a shock bill or interest-bearing refund. A step-by-step guide to filing the change.
Your voorlopige aanslag (provisional tax assessment) is calculated based on a profit estimate you gave—often many months ago when business was different. If your actual profit is now higher or lower, your monthly or quarterly payments may be wrong. The solution is simple: ask the Belastingdienst to adjust it mid-year. This guide tells you when it makes sense, exactly how to file the change, and why timing matters to avoid interest charges.
What is a voorlopige aanslag and why you might need to change it
A voorlopige aanslag is a running estimate of your annual income tax and Zvw contribution (health insurance surcharge), divided into instalments you pay throughout the year. The Belastingdienst issues one based on your prior-year profit—or an estimate you provided when you registered.
The problem: life happens. Your income might surge after a big client win, or collapse if a contract ends. If your actual profit will differ materially from what was forecast, your payment plan no longer fits. You end up either:
- Overpaying monthly, then waiting for a refund after filing your annual return (and earning only minimal interest on your money)
- Underpaying monthly, then facing a surprise bill on 1 May when you file—plus interest (belastingrente) charged daily from the moment you were supposed to pay
Why adjust mid-year
When to adjust your voorlopige aanslag
You should consider an adjustment if:
- Your profit has shifted notably — you now expect to earn significantly more or less than your assessment assumed
- The shift is substantial — a €5,000 difference is probably not worth the admin; a €15,000–€20,000 swing is
- You have visibility for the rest of the year — you can reasonably predict where you'll land by 31 December
- You're paying monthly or quarterly — the more instalments left, the more savings you gain
Do not adjust if you're very late in the year (e.g., November and you haven't earned much) or if your prediction is wildly uncertain. The Belastingdienst can reject frivolous or speculative adjustments, and you might trigger a review.
The impact of belastingrente if you don't adjust
If you under-pay, the Belastingdienst charges you belastingrente (tax interest) on the unpaid balance from the due date until you settle. The rate varies (around 4% annually in recent years, but hedge the exact figure and check belastingdienst.nl)—it compounds daily and adds up quickly on large shortfalls.
Example: You owe €10,000 extra income tax that you didn't pay monthly. If you discover this in May and pay then, you'll owe roughly €400–€500 in interest alone. Adjust your voorlopige aanslag in June when you realized the shortfall, and you can avoid that cost entirely.
Interest runs from the due date, not the assessment date
Belastingrente is not a penalty; it's genuinely owed interest. It starts accruing on the original due date of each instalment, not from when you filed your annual return. The sooner you pay the shortfall, the less interest accumulates.
How to request a change to your voorlopige aanslag
Step 1: Calculate your new expected profit
Before you contact the Belastingdienst, work out your realistic year-end profit forecast. Use your actual figures so far (revenue minus deductible costs) and extrapolate the rest of the year.
A simple estimate: If you've done 8 months of trading and know your profit trend, you can estimate the full year. If January–August profit is €80,000, and September–December usually track similarly, you'd project around €120,000 for the year. Alternatively, if you know a big project is ending or starting, bake that in explicitly.
Include all your estimated deductions:
- Zelfstandigenaftrek (check the 2026 amount on belastingdienst.nl; it's declining annually)
- Startersaftrek (if applicable)
- MKB-winstvrijstelling
- Any other permitted deductions
Step 2: Log in to Mijn Belastingdienst Zakelijk
You request the change online via your Mijn Belastingdienst Zakelijk account (the business portal). You'll need your DigiD or eHerkenning login.
- Go to mijn.belastingdienst.nl
- Log in with DigiD or eHerkenning
- Look for "Mijn aangiftes en aanslagen" (My returns and assessments)
- Find your current inkomstenbelasting (income tax) voorlopige aanslag
Step 3: File a request to modify (wijziging aanvragen)
You do not adjust the assessment yourself; you request a modification. The Belastingdienst will review it and issue a new one if they agree.
In Mijn Belastingdienst, you should see an option to request a wijziging (modification) or aanpassingsaanvraag (adjustment request). Click it and you'll be presented with a form. You'll provide:
- Your new estimated profit (the winst uit onderneming you expect for the full year)
- Your justification — e.g., "A major client contract ended in August, reducing expected annual revenue from €150,000 to €95,000" or "We landed a new long-term client worth €50,000 annually"
- Your recalculated tax and Zvw (the form may calculate this for you; if not, apply the bracket rates and multiply by your revised profit after deductions)
The Belastingdienst may ask for proof
If your change is large or unusual, the Belastingdienst might ask for supporting documentation—e.g., a cancelled contract, a signed letter from a major client, or recent invoices. Have your bookkeeping and key client agreements handy when you submit.
Step 4: Wait for confirmation
The Belastingdienst typically reviews your request within 2–4 weeks. You'll receive a new voorlopige aanslag (beschikking) with the updated monthly or quarterly instalments. Pay the new amount going forward.
If they reject your request, you'll get a letter explaining why. At that point, you can appeal or accept their decision.
An adjustment worked example
Say you're a freelancer with a voorlopige aanslag of €600/month (€7,200/year) based on estimated profit of €80,000. It's now mid-July and you've completed a huge project that nets you €35,000 profit. You now realistically expect €120,000 profit for the full year—a €40,000 upward swing.
Old calculation:
- Estimated profit: €80,000
- Minus zelfstandigenaftrek (2026): ~€1,200
- Minus MKB-winstvrijstelling (roughly 12.7%): ~€10,000
- Taxable: ~€68,800
- Rough tax at ~37% average (hedge this): ~€25,500
- Monthly payment: €25,500 ÷ 12 = €2,125 (simplified; add Zvw too)
New calculation:
- Expected profit: €120,000
- Minus zelfstandigenaftrek: ~€1,200
- Minus MKB-winstvrijstelling: ~€15,000
- Taxable: ~€103,800
- Tax at ~37% average: ~€38,400
- Remaining instalments (6): €38,400 ÷ 6 = €6,400/month
Your instalments roughly double. It stings, but if you don't adjust and under-pay, you'll owe the full shortfall plus belastingrente on 1 May. By adjusting now, you pay the tax on time and avoid interest.
Let ZZP Belasting do the maths
Automatic BTW returns, income-tax forecasts and depreciation — from the invoices you already have.
Try it freeWhat if your profit drops instead?
If you expect to earn less, you can request a downward adjustment. This reduces your monthly payment and improves your cash flow. The Belastingdienst is generally cooperative on downward requests (less risk for them), but again, they may ask for justification if the change is dramatic.
Example: You had a €100,000 voorlopige aanslag based on two major clients. One client ended their contract in April. You now expect only €60,000 profit. Request a reduction; your payments drop accordingly. You'll still have plenty of margin, and if the second client stays, you might actually get a refund at tax time.
Downward adjustments are slower but still worthwhile
Even if it takes the Belastingdienst weeks to approve a reduction, you're building a credit against your final return. Any overpayment you accumulate will be refunded (or carried forward) after you file in May.
Common mistakes to avoid
- Waiting too long: Request your adjustment as soon as you're confident about the change. The later you request, the fewer instalments remain to benefit.
- Being vague: "Business is better" will not cut it. Cite specific events (landed a contract, lost a client, changed your pricing).
- Forgetting your deductions: Your adjustment request should net off all expected deductions (zelfstandigenaftrek, MKB exemption, etc.). The Belastingdienst will recalculate, but showing you know your deductions builds credibility.
- Requesting tiny changes: Adjusting for a €2,000 profit swing costs you time and may annoy the Belastingdienst. Reserve adjustments for material changes.
- Not keeping records: If the Belastingdienst audits your request later, you'll need to justify your estimate. Keep the contracts, invoices, and emails that explain the change.
How an adjustment prevents belastingrente
By adjusting your voorlopige aanslag to match your real profit trajectory, you ensure your monthly or quarterly payments stay in sync with your actual tax liability. This means:
- You avoid under-paying and incurring belastingrente
- You don't over-pay and have to wait for a refund
- Your cash flow is more predictable and fairer
If you later discover your prediction was off—you earned even more—you'll still settle the difference when you file your annual return in May, but at least you've paid most of it on time and minimized interest.
Frequently asked questions
Can I adjust my voorlopige aanslag more than once a year?
What if I adjust and then my profit changes again before year-end?
Do I have to file the adjustment via Mijn Belastingdienst, or can I email or call?
If I don't adjust and owe tax on 1 May, will I get a warning?
Adjusting your voorlopige aanslag mid-year is one of the simplest ways to keep your tax payments fair and avoid shock bills or unnecessary interest charges. The process is straightforward—a form and a justification—and the payoff (avoiding belastingrente and smoothing your cash flow) is real. If your profit forecast has shifted significantly, do not wait for your annual return to settle it. Request the change now and rest easy. ZZP Belasting tracks your profit in real time, so you'll always know when a mid-year adjustment makes sense.