Retention is calculated using the Higher Education Statistics Agency (HESA) methodology of continuation after the year of entry.
Retention figures are available from HESA, as part of the set of Performance Indicators that are released on an annual basis released in March. Non-continuation rates are can be found in Table 3 from the following weblink.
Planning and Business Intelligence reproduce internal retention figures, replicating the HESA figures where possible. The figures are available in Cognos and updated on an annual basis after the HESA return for the previous year has been submitted in November.