Question about paying quarterly taxes.

Hello, this tax year (2025) is the first time I've paid quarterly taxes. My question is this: When I file my final quarterly tax payment in January, am I only to recognize taxes I have to pay up to 12-31-25 OR do I calculate my taxes for 2025 up to 1-15-26 since I'm paying quarterly? I am asking this because I plan on selling a stock at a loss to help out on my taxes owed. Should I sell the stock before 12-31-25 or can I still claim the loss for 2025 if I sell between 1-1-26 thru 1-15-26?