CGT on Selling home That was Rented out

[Martintaxes]

Hello Everyone,
I'm trying to work out my CGT roughly on the potential sale my home that I will have lived in for 18 years and rented it out for 5 years. So total ownership would be 23 years.
Really it's approximate as I'm looking to the future on when best to sell it.
My question is around when I subtract the £12.3k CGT allowance, as this can mean the difference between a fair amount of CGT, versus almost no CGT.

Just using the years rather than months fraction, as it's approximate, and ignoring the 9 months relief for now:-

Let's say, including all start and end costs, my gain was 200k from the sale.
The rental period fraction liable for CGT would be (5/23)*£200k = £43478.

So, do I then calculate my CGT as 29% of £43478, then minus my £12,300 allowance = £12608 - £12,300 = £308?
OR,
would it be (£43478 - £12,300 allowance) x 29% = £8952?

Thank you very much in advance for your help.
Best wishes,
Martintaxes.

[darthblingbling]

Take away from gain first then work out CGT

[Martintaxes]

Thanks very much for your help.