‘The end of July marks another tax deadline – for paying the second instalment towards your 2016/17 tax liability.
If you are required to make payments on account then these are calculated as 50% of your 2016 tax liability each.
The first payment made by 31st January 2017 will always be estimated as it is made before the tax year ends.
While the second payment on account, due by 31st July 2017, is initially estimated. By now you should be in a position to finalise the tax liability after submitting your 2017 tax return.
However, many people make the mistake of not preparing their tax return as soon as possible once the year ends (on 5th April) – as such they could find that they will have overpaid in July.
Also worth noting is the fact that the second payment on account will not increase beyond the initial amount estimated – so there is no disadvantage to submitting your 2017 tax return as soon as possible.’