Next Sunday's tax bill

Next Sunday, July 31, the second payment on account of 2015/16 tax is due. Unless you have already submitted your 2016 tax return (full marks if you have) then the payment will be based on your 2015 tax bill.

If your 2016 tax bill will be less than your 2015 bill you'll end up paying more tax than you need. To avoid this you can either submit your return so that HMRC will correct the amount due or you can ask for the payment on account to be reduced.
Just be careful that you don't reduce the instalment to below the actual amount due otherwise HMRC will charge you interest (and possibly a penalty).

Days to January 31st