How we keep everything current
Which data updates itself, which rates we check by hand every year and what Last reviewed means on a tool.
Sumish has two kinds of tools. Calculators work with your input and with fixed rules, such as a tax rate. Lookup tools look something up in open data, such as a licence plate (kenteken) or the figures for your neighbourhood. Both have to match how things are now. This is how we make sure of that. What you can see of it on the page is in How we make sure data stays current and checked. How a result comes about, you can read in How our calculators work.
Data that updates itself
The open data of the lookup tools is in our own database. It fetches every source again at a fixed rhythm:
| Source | How often | More explanation |
|---|---|---|
| Vehicle register of the RDW (the Dutch vehicle authority) | every week; APK (periodic inspection), export and recalls with every search | The RDW data |
| Prices from Statistics Netherlands (CBS): inflation, fuel and energy | fetched every day; CBS updates pump prices weekly, CPI and energy rates monthly | CBS prices |
| Weather measurements from the KNMI (Royal Netherlands Meteorological Institute) | every morning | KNMI weather data |
| Core figures per municipality (gemeente) from CBS | every week | CBS figures about neighbourhoods and municipalities |
| Neighbourhood map, postcode figures and neighbourhood per address from CBS | per year, as soon as there is a new version | CBS figures about neighbourhoods and municipalities |
| Addresses from the BAG (the Dutch basic registration of addresses and buildings) of the Kadaster (the Dutch land registry) | every month | Maps and addresses |
| Parking garages and park-and-ride (RDW), charging points (NDW, the Dutch national road traffic data service) and filling stations (OpenStreetMap) | every month | Parking, charging points and filling stations |
This is how a load of new data goes:
- We fetch a full, new copy. We do not update bit by bit.
- We check the copy. Are all fields still there? Are the counts within the expected limits? Has no table suddenly become much smaller?
- Only when everything is right do we swap the old data for the new in one go. If something is wrong, the old data stays. So you never see a half load.
For the figures that appear per year, our system checks every week whether the source has a new year or a changed file. Before we load a new year, we read the source's terms of use again. We do that at least once a year in any case.
Monitoring
Every quarter of an hour the site checks whether the database is healthy. If something goes wrong, we get an email. For example if:
- a load was too long ago, or keeps failing;
- a series from CBS is behind for longer than normal;
- we have not read the terms of use of a source for more than a year;
- the database does not respond.
If the database does not respond, a lookup tool says that searching is not possible right now. The calculators keep working.
What you see on the page
Below every lookup tool is the block About the data. There you see two dates:
- how far the data runs: the state of the source, such as the last day with a pump price;
- when we fetched the data: our last load, and how often we do that.
The two are kept apart on purpose. We can fetch today while the source still has figures from last month.
Rates we update by hand every year
Some calculators work with rates from the law or from the government. They usually change once a year. Think of the road tax calculator (Dutch edition), the net salary calculator, the allowances (toeslagen) and the maximum mortgage calculator (Dutch edition). We do not fetch such rates automatically. We look them up in the official source and check them.
- Review date. Every calculator with such rates has a date on which we have to check it again. A month ahead we see that in our admin. On the day itself we get an email.
- Maintenance note. For every calculator with rates, our work log says when the new rates arrive, which sources we use, what we have to change and how we check it.
- One calculation as the basis. 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.
- After the check we move the review date forward and update Last reviewed.
Most rates change on 1 January. The lending limits for a mortgage appear in November, and the yearly index of CBS for the Money Then and Now calculator in February.
How we check a calculator
If an official source gives a worked example, we adopt it as a fixed test. A few examples:
- Road tax: the Tax Administration's (Belastingdienst) example for a petrol car of 1,100 kg in Gelderland, €126 per quarter in 2026.
- Net salary: every row of the Tax Administration's white monthly table.
- Healthcare allowance, child-related budget and rent allowance: the worked examples from the Benefits department (Dienst Toeslagen).
- Transition payment (transitievergoeding): the maximum from the Dutch central government (Rijksoverheid), €102,000 per 1 January 2026.
We also compare with other calculation tools. The CPI indexation calculator (Dutch edition) gave exactly the same result as the CBS tool itself for 49 combinations on 11 October 2026.
At every publication all tests run automatically. If one fails, the calculator does not go live. The calculation core exists twice: 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. You can read more on the How we work page.
What Last reviewed means
At the bottom of the page of a tool is Last reviewed, with a date. That is the day we last really checked the content: the sources, the rates, the calculation rules and the texts. It is not the day of the last publication, because that shifts with every small improvement. We only move the date forward after a real check.
With a lookup tool the data updates itself. There Last reviewed says something about the tool itself: the method, the texts and the sources. How current the data is, you see under About the data.
If something substantial changes, such as a rate or a new choice, it is listed with the date under Changes.
Spotted a mistake?
Is something wrong, or are you missing a source? Let us know via the contact page. We look at every report.
The Sumish editorial team
More guides
- DataCBS figures on neighbourhoods and municipalitiesWhere the figures for neighbourhoods, districts and municipalities come from, which year they are from and why CBS sometimes keeps a figure secret.
- DataMaps and addresses: PDOK and the KadasterWhere the map, the addresses and the postcodes on Sumish come from, and why the map runs through our own server and passes nothing on about you.
- How we workHow we make sure data stays current and checkedWhat you can see of the review date, the values with an effective date and the data that updates itself, and what we do when a source goes quiet.