Free self assessment tax calculator

[Pistonpants]

I’d like to work out how much I’m likely to owe HMRC for this tax year and then play around with paying different lump sum amounts into my pension to minimise this.

Obviously I can do this with the gov.uk online self assessment but I’m guessing for this tax year it won’t go live until it’s too late to make a pension payment in this tax year.

Basically need an online/offline version of the gov.uk self assessment form/calculator that I can play around with now before the 5th April.

Any suggestions?