to be paid. These are the Lower Earnings Limit (LEL), Primary Threshold (PT), Secondary Threshold (ST) and Upper Earnings Limit (UEL), though often the PT and ST are set to the same value. The cash value of most of these figures normally changes each year, either in line with inflation or by some other amount decided by the Chancellor. The PT is normally indexed to inflation using the CPI, while other thresholds remain indexed using the RPI. On earnings below the LEL, no NICs are paid because no benefits accrue on earnings below this limit. On earnings above the LEL, up to and including the PT, employee contributions are not paid but are credited by the government as if they were (enabling certain low-paid workers to qualify for benefits). On earnings above the LEL, up to and including the ST, employer contributions are not paid. On earnings above the PT/ST, up to and including the UEL, NICs are collected at a rate which is determined by a number of factors: Whether the employee has reached the age at which State Pension becomes payable Whether the employee is a married woman paying reduced-rate contributions. This facility was abolished on 11 May 1977 but women who were already paying these contributions at that time were allowed to opt to continue to do so for as long as they remained married and in employment Whether the employee is an ocean-going mariner or deep-sea fisherman. In the case of the employer contribution, whether the employee is aged under 21 or is an apprentice aged under 25. On earnings above the UEL yet another set of rates apply, this time depending only on whether the employee has reached the age at which State Pension becomes payable or is an ocean-going mariner or deep-sea fisherman Table letters As indicated above, the rates at which an individual and their employer pay contributions depend on a number of factors. Consequently, there are many possible sets of employer/employee contribution rates to allow for all combinations of the various factors. HMRC allocate a letter of the alphabet, referred to as an 'NI Table Letter', to each of these sets of contribution rates. Employers are responsible for allocating the correct table letter to each employee depending on their particular circumstances. Each tax year, HMRC publish look-up tables for each table letter to assist with manual calculation of contributions, though these days