Are you self-employed? If you are, you may need to make your second payment on account for 2016-17, due date for payment is 31 July 2017.

This second payment on account will have been based on 50% of your combined Self Assessment tax and Class 4 NIC liability for 2015-16. Which raises an interesting question.

What if your actual Self Assessment liability for 2016-17 is higher or lower than the liability for 2015-16? From a cash flow perspective, the outcome is win-win in both cases. Let’s consider the two options in more detail:

2016-17 liability is higher than 2015-16

In this case your taxable profits will have increased, year on year, and after your January and July 2017 payments on account have been deducted, there will be a balance owing to HMRC. At present there is no legal requirement to add this underpayment to your July 2017 payment, in fact HMRC will not ask for any balance owed until 31 January 2018.

2016-17 liability is lower than 2015-16

In this case your taxable profits will have reduced, year on year, and if you make your January and July 2017 payments on account (based on the 2015-16 results) you will have overpaid HMRC. Again, there is no legal requirement to change your July 2017 payment, and HMRC would no doubt be happy to make use of your overpayment until they would be required to offer a possible refund on 31 January 2018.

However, if you find yourself in this position, you can make a formal application to reduce your 31 July 2017 payment.

Our advice, if you have a realistic expectation that your accounts on which your 2016-17 liability will be based (usually the accounts ending in the tax year to 5 April 2017) are lower than the previous year, then we should calculate the effect on your Self Assessment liabilities for 2016-17 and lodge a formal request to reduce your July 2017 payment on account, if appropriate.

Apparently, over 4 million tax payers are eligible to claim the new marriage allowance, but only 2 million have done so. If our math is correct, this add up to £1.3bn in unclaimed tax refunds.

The allowance has been available since 6 April 2015 and is worth £212 for 2015-16, £220 for 2016-17 and £230 for 2017-18; a cumulative tax rebate of £662. The allowance is only available to the following couples:

• Couples must be married or in a formal civil partnership, living together does not qualify.
• One spouse/partner needs to be a non-tax payer. i.e. their income must be below the personal tax allowance. (£10,600 for 2015-16, £11,000 for 2016-17, and £11,500 for 2017-18).
• The other spouse/partner needs to be a basic rate (20%) taxpayer. Higher rate taxpayers cannot receive any benefit from the Marriage Allowance.

The spouse/partner that has the spare personal allowance needs to make the claim, and once made, the relief should automatically be given in subsequent years. You will need to advise HMRC if your circumstances change.

The allowance is simple to claim, just visit the Gov.uk website at https://www.gov.uk/apply-marriage-allownce. And don’t forget, it is the spouse partner who pays no tax (with an unused, or partially unused, personal allowance) that needs to make the claim.

Before making the application you will need to have you and your partner’s National Insurance numbers. You will also need a way to prove your identity. This can be one of the following:

You’ll get an email from HMRC confirming your application.