The coding threshold entitles taxpayers to have tax underpayments collected via their tax code, provided they are in employment or in receipt of a UK-based pension. The coding process applies to certain debts such as Self-Assessment liabilities, tax credit overpayments and outstanding Class 2 NIC contributions. Instead of paying off debts in a lump sum, money is collected in equal monthly instalments over the tax year.The amount of debt that can be coded out ranges from £3,000 to £17,000 based on a graduated scale. This is a different limit to that for paying your Self Assessment bill where the amount owed must be less than £3,000. The maximum coding out allowance only applies to taxpayers with earnings exceeding £90,000. The full breakdown is as follows:EarningsCoding out limitLess than £30k £3k£30k to £39,999.99 £5k£40k to £49,999.99 £7k£50k to £59,999.99 £9k£60k to £69,999.99£11k£70k to £79,999.99£13k£80k to £89,999.99 £15k£90k or more £17kTaxpayers with underpayments in the tax year 2017-18, have until 30 December 2018 to file their Self-Assessment returns in order to have the monies collected in the 2019-20 tax year starting on 6 April 2019.