Self employed 1 day/ week - tax return question

[DangleDonkey]

Hi everyone,
I run baby classes one day a week alongside my normal job (2.5 days). I started this self-employment in September 2023 and I'm trying to keep on top of business records for when I need to do the dreaded tax return.
How do car expenses work here? I know I can do the 45p per mile flat rate and in reality that might be what I claim, but I'm using the gov.uk tool to see if simplified expenses are the way to go and therefore want to put in the full figures to compare. Would I put in all my car costs (petrol, insurance, repairs, MOTs etc) or my car costs divided by 7 as I only work that one day in my business? Because they're classes at set times on set days, there's no grey area really on how much I use my car for my business.
Appreciate any advice here! Thank you

Would I put in all my car costs (petrol, insurance, repairs, MOTs etc)

No, not unless you use the vehicle 100% for the business. Those are predominantly private expenditure items. I think 1/7 would likely be a massive overstatement too.

What do you actually use the car for for the baby classes? Have you tracked your business mileage? You can't claim for travel between home and work.

If you haven't tracked it then you're going to have a hard time supporting the claim, especially an aggressive claim like 1/7 of all the vehicle costs.