Is my net income and reserved income tax always correct?

The short answer is: yes and no.

NettoWise calculates your net income and your income tax reservation based on two things: the tax rules for the selected year and the financial data you enter.

In most situations this gives a solid indication. But it remains a calculation with assumptions. If data is missing, entered incorrectly, or your situation falls outside what NettoWise currently supports, the outcome can be higher or lower than what you eventually see in your tax return.

If you are unsure how to interpret the result, or your situation is complex, it is wise to have a tax advisor take a look.

Why "correct" can be tricky

Income tax is not a monthly final number. It is ultimately a yearly settlement. A monthly calculation is therefore always a snapshot that reflects what is known so far.

That means you might see a very different reservation in January than in November without anything being "wrong". Your year-to-date picture is simply becoming more complete.

NettoWise is built so that by the end of the year it should match based on the financial data.

When results can differ

Below are the most common causes.

1. Input is incomplete or incorrect

NettoWise calculates with what you have recorded. If certain costs are not entered yet, or amounts are entered incorrectly, that affects your profit and therefore your tax reservation.

2. Your situation is not fully supported yet

NettoWise is a young company and grows step by step. Some fiscal situations and exceptions are not implemented yet, or are handled in a simplified way.

If your situation falls into that category, the calculation can differ from the final tax return.

We are working hard to add all situations for sole proprietors to NettoWise. This will happen later this year (2026).

3. Rounding differences

NettoWise calculates in cents, while the income tax return uses whole euros. That can result in a difference. It should not be large and will usually be limited to a few euros.

What you can expect from NettoWise

NettoWise aims to be as predictable as possible. If your input is correct and your situation is supported, the outcome is a strong indication of your net income and your income tax reservation.

We are continuously expanding support for sole proprietors. Later this year (2026), new situations will be added.

There will also be a clear list of the situations that are still missing, so you know the current boundaries.

What this means for other tools

This is not unique to NettoWise. The same principle applies to accounting tools, calculators, and even the online tax return itself.

Every tool calculates based on the information you provide. If that information is incorrect or missing context, the outcome can differ. That is why it remains important to check your numbers regularly and seek advice when in doubt.

A helpful tip if you want to verify

Want a quick check to see if the calculation makes sense?

• Check whether your total profit to date is correct.
• Check whether major costs and deductions are entered.
• Check whether your periods align with what is in your accounting tool.

If something looks off there, the difference is likely coming from the input rather than the calculation.

Questions?

If you have other questions, you can always reach our support.