Free tool

F10 notification checker

Put in the programme and the numbers, and the checker runs both regulation 6 tests and shows the arithmetic.

How many working days will the construction work last?

Working days on site, not calendar days, and not the whole design programme.

At the busiest point, how many workers will be on site at once?

Everyone working on the site at the same time, including subcontractors.

On an average working day, how many workers will be on site?

Used to estimate person days. If you already know the person day total, put it in the box below instead.

Person days, if you already know the figure

Optional. Overrides the estimate above.

This tool gives general guidance from the answers you type. It is not legal advice about your project, and it cannot see your drawings or your site. Where a project is unusual the answer is a conversation rather than a checker. How we write this.

The two tests, in the regulation's own shape

Regulation 6(1) of CDM 2015: a project is notifiable if the construction work on a construction site is scheduled to last longer than 30 working days and have more than 20 workers working simultaneously at any point in the project, or exceed 500 person days.

The first is an and, not an or. Both halves have to be true at once. The second is a total across the whole project.

Worked examples

ProjectDaysPeakPerson daysNotifiable?
Domestic rear extension606240No
Whole house refurbishment12010720Yes, on person days
Fast track office fit out2530750Yes, on person days
Small housing scheme180252,700Yes, on both

What notification does not decide

Most domestic projects need all three and are not notifiable.

Written by James Nicholson, BSc (Hons) Architectural TechnologyLast reviewed 28 August 2026How we write this

Sources

  1. CDM 2015, regulation 6 legislation.gov.uk
  2. CDM 2015, regulation 7 legislation.gov.uk
  3. HSE: how to notify a project (F10) hse.gov.uk