Pretty much work out my outgoings, expenses and what I get in.
Outgoings is the usual, mortgage, insurance, factors fees. Also keep allreceipts for any work, repairs of furniture I’ve had to buy. Wear and tear to fixtures and fittings is deductible too at 10% per year but I haven’t needed to include this in my calculations up till now.
Just jot down the totals when prompted to, and file away all my paperwork once it’s done. I slways keep my P60 so I can note down my income and tax paid from my main employment. Don’t know if that will apply in your case.
Was a bit daunting the first time I did it but my biggest problem the last couple of times has been remembering my password!
Edit- sounds like you’ve got it sussed!