Another tax/working tax credits question

[ImYourWomanJonSnow]

I work part-time for an employer and one day a week on average as a freelancer (it's rather unpredictable - and dwindling - strand of work: last year I only brought in £500). I just received my P60 for 2017 and it turns out that I have underestimated my total for the year by about 1.5k (it comes to £16,950). I receive working tax credits, child tax credits and we also received free 15 hours childcare for families with income under 16K.
My laptop (that I use both for personal and freelance) is on is last legs - would it be a claimable expense if I bought a new one, bringing my total for the year down?

I presume so - I always put office equip down as a loss

I presume so - I always put office equip down as a loss. Keep your old one for personal use & buy a new one for work

Would you not have had to buy it before the end of March?

I don't think you can put it down for the 2016/17 tax year if you buy it now but I don't see a problem in a % of the cost for the 2017/18 year. If you use it 50/50 business and personal use then 50% of cost is allowable etc.