Employer National Insurance 2025

Hello, I have a few questions for the new tax year that I am a little unsure of, If I have an employee who has 2 jobs, their first job being with another company & their second job with me. If they go over the NI threshold with their first job (not with me) would we then also pay NI even though they have not gone over the NI threshold with us? Is national insurance accumulative like tax? If I have a casual worker who works 40hrs one week and 2 hours the next, is the NI adjusted per wages every week? Thanks

Hi CJHL1947,
If an employee has another job or jobs with a different employer or employers, work out National Insurance contributions in the normal way on the earnings you pay the employee. Ignore the payments made to the employee in the other job(s).
However, if you carry on business in association with the other employer(s), you must add together the earnings from each job and work out National Insurance contributions on the total unless it’s not reasonably practicable to do so. You may be asked to show why it has not been practicable to add together the earnings from each job.
Employers are considered to be carrying on business in association with each other if:
• their respective businesses serve a common purpose
• to a significant degree, they share such things as accommodation, personnel, equipment or customers
You can find more information in the National Insurance Manual. 
Guidance is available at: 
•    NIM10000 - Aggregation of earnings: contents - HMRC internal manual.
Thank you