What category does Tax come under?
Taxes can be viewed as a deductible liability depending on the timescales involved.
For example, say you have a tax bill which is due in December 2014 and another in January 2015 and this amounts to £4000. Do you still need to pay Zakat on that?
In this case, since this liability is known and is due for payment, albeit the deadlines being in 5-6 months, it is permissible for you to deduct this amount from your other assets before you calculate your Zakat. The safer thing to do is to include this money in your calculation, especially if you don’t feel that paying Zakat on it will in any way delay or impede you in clearing the liability when the time comes. But as mentioned deduction would be permitted in this case. Again, it all comes down to the individual’s intentions and conscience – be honest with yourself! Allah knows. Alhamdullilah!