Time limits for best judgment assessment vary by assessment year, with a TPO reference granting an extension. Limitation periods for best judgment assessments vary by assessment year: up to and including 2017-18 - 21 months from end of that assessment year; 2018-19 - 18 months; 2019-20 and onwards - 12 months. A reference to the Transfer Pricing Officer extends the period for assessment by a further 12 months.