Self assessment utilities/ mortgage

[Christmascookiesmmmm]

Hi! I’d be super grateful for any advice!!
Doing self assessment. I work partly employed and partly as a private tutor from home for about 13 hours a week. I also do planning for my paye job at home, probably around 6-8 hours a week. For household expenses, I’ve always put the flat rate down of £18 a month, but I feel like I should probably be able to claim more now we bought a house december 2018 and I basically chose it based on my job, we definitely wouldn’t have bought as big a house if it wasn’t for having to work from home! Also I use a lot more heating than normal with clients in etc.
The figures are : mortgage over 35 years, £830 a month split between me and partner so I pay £415 a month,
House is 3 bed, 2 reception rooms, 1 bathroom and kitchen, and I use one of the reception rooms to tutor in (it also has dining table in but main purpose is tutoring and like I said we wouldn’t have gone for 2 reception room house if I didn’t tutor)
Then we have utility bills obviously.
Just wondered how I work out what percentage I can claim? I’ve looked online and really can’t find anything to help! All I can find just says I need to work out what percentages are used etc!
Thanks so much!!

You can only claim for mortgage interest and you don't need to split it to your half. I work mine out based on how much of the house is used solely for business use and for how long. For example, my workroom is 1/6th of the house. I use it solely for business 8 hours a day, so 1/3rd of a day. I then calculate based on how many days in a month I used it for that. I only claim for gas/electric, mortgage interest and broadband. Anything else is negligible. I also have my business and home insurance under one policy, so claim the full business proportion. I did check whether I could claim any portion of the house insurance as it is much higher than an average policy, just because I work from home. I was told I couldn't.
My utilities and mortgage interest only come to around £19 a month and I work from home full time (I should really be claiming the flat rate). Given how much work you do from home I wouldn't see you using more than £18. £18 is actually very generous for 20 hours a week.

All I can find just says I need to work out what percentages are used etc!

Which is how you have to do it. As said above, you take the space used in your house for your business and then also the time spent in that space, all compared with the space not used for business and the time it's not used. Unless you have a dedicated room that isn't used for anything else, for several hours per day, your claim is going to be pretty low and may not be that much different from the HMRC scale/approved rates. No one else can do the number crunching for you - it's all based on the facts of your usage and the costs you're incurring.