When does the 5years calculation starts when calculation for ILR application?

Hi all!

I switched from tier 4 (student) to tier 2 general. When I switched it took almost 5 months of time for my application to be processed. My question is when I have to apply for ILR which date should I use to calculate the 5 years stay. Should it be my COS start date or BRP start from date? The difference is almost 6 months

Can someone help me with this, please?

Thanks in advance.

It counts from Tier 2 visa start date. Your cos start date is irrelevant as having a cos assigned does not mean you have a visa.