Reference year and reference date in the PSO Performance Ladder
The reference year is the twelve months before the reference date. In that year, the PSO measures how many people from the target group worked for you and how big your company was. The reference date is the moment that measurement ends. According to section 1.5.2 of the PSO manual 2.6 from TNO , the reference date may be no more than three months before your final application. Your level therefore depends on one year of data, not on your current situation. For how the level follows from that, see PSO levels and calculation. For who counts as a worker in that year, see company size in the PSO. The steps to apply afterwards are on applying for a PSO certificate and costs.
A common mistake is entering your current number of employees. That is not what the PSO measures. Every figure in your calculation tool belongs to the reference year.
On this page
- What is the difference between reference year and reference date
- An example with the dates
- Employees who start or leave mid-year
- What you enter per period
- Common mistakes
What is the difference between reference year and reference date
| Term | What it is | Example |
|---|---|---|
| Reference date | The moment the measurement ends | 1 January 2027 |
| Reference year | The twelve months before the reference date, over which you measure your data | 1 January 2026 to 1 January 2027 |
| Application date | The day you submit your final application in MijnPSO | Sometime in spring 2027 |
The reference date may be up to three months before your application date. A company that applies in March can therefore use a reference date of 1 December or later. This keeps the measurement current, without you having to update your annual figures every month.
The reference year is not your financial year. It is the twelve-month period that ends on the reference date. It can therefore fall in the middle of a calendar year.
An example with the dates
Suppose a company wants to submit an application in February 2027. The reference date is 1 January 2027. The reference year is then 1 January 2026 to 1 January 2027.
In that year, the company had the following people from the target group (fictional):
- An employee who worked from 1 March 2026 to 1 January 2027: counts for ten of the twelve months.
- An employee who started on 1 July 2026 and still works there: counts for half.
- An employee who left in May 2026: counts for the part up to that date.
The weighting an employee receives depends on their starting position and the type of contract. That is set out on PSO levels and calculation. This section is about the period over which you count.
Employees who start or leave mid-year
The manual uses the number of placements in the reference year as its starting point. Someone who starts halfway through the year therefore counts for half. The same applies to someone who leaves halfway through. An employee who worked the whole reference year counts in full.
This makes your files important. For the auditor, you must be able to show the start date and the end date for each employee. The manual lists this as one of four details that must be correct in the sample. See PSO audit: how does the audit work?.
What you enter per period
Not everything in the calculation tool uses the same period. An overview:
| Detail | Period | Note |
|---|---|---|
| Target group employees | Reference year | Weighted by time in the reference year |
| Company size (number and FTE) | Reference year | Average over the measurement moments |
| Purchasing from PSO suppliers (indirect) | Reference year | Excluding VAT, invoices from the reference year |
| Number of FTE for the two-FTE requirement | Reference year | The threshold applies to the reference year |
| Number of people on the application date | Application date | A snapshot on the day you submit |
| KvK registration of one year | Application date | Applies to a level, not to Aspirant status |
Pay attention to the last two rows. The KvK requirement and the number of people on the application date are snapshots. The rest concerns the reference year.
Common mistakes
- Entering your current staff numbers. That is the number from today, not from the reference year. The figures often differ.
- Choosing the wrong reference date. A reference date more than three months before the application is not allowed. Plan your submission close to the reference date.
- Treating the financial year as the reference year. The reference year ends on the reference date, which does not have to be 31 December.
- Counting employees who joined mid-year in full. They count only for the part of the year they worked.
Measurement moments and fluctuation
Company size is an average over the reference year. How often you measure it depends on how much your workforce fluctuates. The manual gives three rules of thumb in section 3.5.3:
| Variation between the lowest and highest number of employees | Number of measurement moments |
|---|---|
| Less than 10% | Two: at the start and end of the reference year |
| Between 10% and 30%, seasonal effects or changing flexible staffing | At least four, for example per quarter |
| Strong fluctuations, as in temporary staffing agencies | Monthly measurement makes sense |
The number of moments must match the variation and be verifiable for the auditor. If it is difficult to calculate the average across the whole year, you may add up monthly averages and average them into a yearly average. This stops one busy month from skewing your average.
For the auditor, this means they want to see how you chose your measurement moments. A short note with the reason is therefore useful. For example: “We had a lot of temporary inflow in the reference year, so we measure per quarter.”
Checklist for the reference date
Use this list before you record your reference date in the calculation tool:
- Is the reference date no more than three months before the day you submit your final application?
- Does the reference year match the twelve months before the reference date?
- Do you have a start date and, where applicable, an end date for each target group employee?
- Did you average the FTE over the reference year, and not use today’s figures?
- For the indirect contribution, did you use only invoices from the reference year?
- Did you keep a note for each employee explaining why they started or left mid-year?
If you answer no to any question, fix it first. A wrong reference date is hard to correct afterwards.
What the auditor asks
The auditor checks the assumptions you made in the calculation tool. In a sample of files, they look at the start and end dates. These must match what you entered. If a date is missing, the employee may drop out of the count. So make sure the dates in your personnel records are correct before you plan the audit.
Further reading
- Company size in the PSO describes how the FTE in the reference year is calculated.
- Applying for a PSO certificate and costs sets out the steps in which you choose the reference date.