https://help.gosimpletax.com/hc/en-gb/articles/200355859-Computer-or-Laptop
Can I claim?
Yes.
Conditions
Your business is sure to make use of a computer or laptop so yes, you can claim. If business use is 100% then claim the full purchase price. However, if you use it for both home and work then you can only allocate a percentage to the business to offset against your tax. For instance, if your new computer cost £800 and business use is 40%, only £320 can be entered into your accounts.
On SimpleTax
It will be allocated under the heading of: Self-Employed Expenses - Computer and Office Equipment - Computer.
***
More information
Should you put pre-used items in for business use, or buy second-hand office items from somewhere like EBay, then you need to assess the market value, for instance:
The new computer may be £800 in the store, but you bought a used computer on EBay for £450 with a business usage of 40%, this allows you to allocate £180 as a business related cost.
Similarly, if you are using an old computer or laptop as business equipment, you cannot charge the as-new price to the company if the item is several years old. You will need to establish the as-new price and deduct a percentage for how old the product is. This is the cost you can offset against the business. Again if you are struggling to work out a second-hand price, look on some of the internet sales site for used items to give you a price.
other keywords: CPU, PC, mac, apple, machine, gadget, macintosh, desktop, workstation, portable, palmtop, device