How our calculators work and how reliable a result is

A calculator gives you a number. Here you can read how that number comes about, how solid it is and what happens to your input.

How this number is calculated

Below a result you find the block How this number is calculated. It works through the steps with your input: the intermediate steps, the formula with your numbers filled in and the final result. It is not an explanation beside the calculation but the same formula that works out the result. Change a number and the block changes with it. That way you can check every step yourself, for example with the net salary calculator or the healthcare allowance calculator.

• The same formula twice. The calculation core runs in your browser and on our server. With every new version of the site we check that both give the same result down to the last decimal.
• Tested against official examples. See How we check.
• Assumptions and sources. Below every calculator you find what we assume, which sources we use and when we consulted them. There you also see what a result leaves out.

You can read more about our way of working on the How we work page.

Indication, worked example or guideline

Below a result is a short text that says how to read it. There are three kinds:

Lookup tools and tools with prices or figures from a source have their own text. It says, for example, that a pump price is a national average, or that the figures from Statistics Netherlands (CBS) cover the whole neighbourhood and not a single address.

Rounding, and why another amount may differ

• Intermediate steps stay unrounded. We only round at the end, to the number of decimals that suits the result, such as whole cents. If the official calculation itself rounds a step, or rounds it down, we do the same. For the healthcare allowance (zorgtoeslag), the amount per month is a twelfth of the yearly amount, rounded down.
• Halves go up. We round the way an accountant does: 2.5 becomes 3 and half a cent goes up. Computers sometimes turn 1.005 into 1.00499999 internally. We clear up that noise first, so 1.005 becomes 1.01.
• Another party may round differently. A bank, the Tax Administration (Belastingdienst), the Benefits department (Dienst Toeslagen) or a calculation tool from CBS may round a step earlier or later, count days differently or use its own rate. As a result their amount can differ from ours by a few cents or a euro.
• Rounding a ratio is also a choice. With the CPI indexation calculator (Dutch edition), CBS rounds the ratio of two index figures to three decimals. We do the same, so we arrive at the same result to the cent.

A result is an indication. The Benefits department determines an allowance, a bank makes an offer, and an insurer or employer calculates with its own terms. If you need the exact amount, the amount from that party applies.

What happens to your input

• You calculate in your own browser. What you enter does not come to us, and we do not store or log it.
• If calculating in your browser does not work, our server calculates along. It uses your input only to send the result back and does not keep it.
• In the link. With most calculators your input is in the link after the # sign, so you can share a calculation. Your browser does not send that part to the server. With calculators about health, such as BMI, your input is not in the link.
• Lookup tools such as a licence plate (kenteken) or a postcode do send those to our server, only to answer that one question. We do not keep them.

Everything is on the privacy page.

How we check

• Official examples as a fixed test. If an official source gives a worked example, we adopt it. For example the Tax Administration's example for road tax, every row of the white monthly table for the net salary calculator and the worked examples from the Benefits department for the allowances.
• All tests at every publication. If one fails, the calculator does not go live.
• An independent calculation. We build calculators with many tables with a script. That script produces both the calculation rules and the expected results of the tests from one independent calculation.
• Comparing with another calculation tool. The CPI indexation calculator (Dutch edition) gave exactly the same result as the tool from CBS for 49 combinations on 11 October 2026, to the cent.
• Rates and figures. We take rates set by law from the official source and put a review date on them. How that works, you can read in How we keep everything current and in How we make sure data stays current and checked.

Do you think something is wrong? Let us know via the contact page. We look at every report.

Tools for this guide

• Net Salary Calculator Netherlands (Gross to Net, 2026)Gross to net per month, 2026
• Healthcare Benefit (Zorgtoeslag) Calculator Netherlands 2026Healthcare benefit per month and per year, 2026
• Car Costs per Month Calculator NetherlandsAll the costs of your car in one total

The Sumish editorial team