Keeping a mileage log is not mandatory, unless you make use of specific schemes for which a mileage log is required. For example, if you do not pay any tax on the private use of a company car, you are required by the Tax and Customs Administration to keep a mileage log. There may be other reasons why keeping a mileage log is mandatory.
Before we continue, we'd like to explain what a mileage log actually is. It's a record of all trips and kilometers driven with a car. It records the time a trip started, the address (including postal code and house number), how the trip was driven, where the trip ended, how many kilometers were traveled, and possibly even the driver. A mileage log also contains vehicle information. Depending on the application for which a mileage log is kept, there are many or few requirements regarding which data is recorded.

If no additional tax is paid for private use of the company car, the Tax and Customs Administration requires a mileage log. A "Declaration of No Private Use of the Car" is signed for this purpose. The maximum annual private mileage allowed in the company car is 500 kilometers. This can be demonstrated by keeping a mileage log.
If you drive business miles in a private car, you can claim these kilometers from your company or employer. To do this, you need a mileage log to justify the kilometers driven and the corresponding mileage allowance.
If the company car is also used privately, VAT must be paid for private use. This is a standard amount of 2,7% of the list price. However, if you can demonstrate how much private use is involved, this amount is waived, and the VAT portion is calculated proportionally to actual private use. You can demonstrate this with a mileage log.
Do you own or operate a passenger car, van, or motorcycle with a foreign license plate? Then you are eligible for the employer's exemption (BPM) if you live in the Netherlands and meet the following conditions. To take advantage of this scheme, you must demonstrate, through a mileage log, that you have used the car abroad for at least 50% of your journey.
These are the regulations that require mileage tracking. There are also several other reasons and benefits to keeping a mileage log, such as providing insight into mileage driven for employer car schemes or as an efficiency tool.