Steps:
The employer and the employee need to contractually agree on the 30% ruling in the contract of employment;
The employer and the employee gather the information and documents required for the filing of the application for the 30% ruling;
The application is filed with the Dutch tax authorities (needs to be done within 4 months of first arrival in the Netherlands);
The Dutch tax authorities will make a formal descision on the application within 6-12 weeks;
Once granted, the 30% ruling needs to be implemented in the salary administration to effectuate the benefit.

Addendum to contract of employment
The employment contract should be updated to include an article agreeing on the 30%-ruling applicatio, payroll implementation and agree that the minimum taxable salary is met. If the contract has already been signed, then the 30%-ruling article can be stated on a separate letter that can be attached to the existing contract as an addendum.

Information needed for the 30%-ruling application

• full details of the employer including company address and Dutch wage tax number;
• full details of the employee, including address;
• the Dutch tax number so-called burgerservicenummer (BSN ;
• copy passport of the employee;
• a copy of the residence permit and work permit (if applicable);
• the curriculum vitae of the employee;
• a copy of the employment contract, including the 30%-ruling agreement/addendum;
• a power of attorney signed and dated by a representative of the employer;
• a power of attorney signed and dated by the employee;
• proof of the employee's residency abroad for each month in the 2 years prior the the employment start in the Netherlands.

Filing timeline for the 30% ruling.

General
If granted, the 30% ruling will be effective as of the first of the month following application. For example:

• If the application is filed on November 23,  the ruling is effective as of December 1st.
• If the application is filed on April 1, the ruling is effective as of May 1st.

4-month exception
An exception to the general rule is that if the application is filed within 4 months after the start of the employment in  the Netherlands, the 30% ruling will have retroactive effect to the employment start date of the employee. For example:

• The employee starts working in the Netherlands on February 12. The application is filed on May 13 (within the 4-months). If granted, the 30% ruling will be effective as of February 12.
• The employee starts working in the Netherlands on February 1. The application is filed on June 2nd (outside the 4-months). If granted, the 30% ruling will be effective as of July 1.

Formal decision tax authorities on 30% ruling

The Dutch tax authorities will generally review the application within 6 to 12 weeks. They can either approve or deny the 30% ruling or they may request additional information:

Approval
If approved, the 30% can be applied in the Dutch payroll. The benefit will be calculated retroactively (if filed within the 4-months) through the payroll and refunded to you with your regular salary.

Denial
If the 30% ruling is denied, you have the right to file a letter of objection against the decision. This needs to be done within 6 weeks of the decision . The tax authorities will also indicate the grounds for denial. These grounds can be contested in the letter of objection by providing additional information. If the tax authorities also deny the 30% ruling based on the letter of objection, then you can have the matter appealed in court. The appeal needs to be filed within 6 weeks of the second denial.