This contribution outlines a strategy for assessing tritium (T) inventory in plasma facing components (PFC) during JET T operations. It is based on retention as a fraction of fuel injected in-vessel, currently reported as 0.24% for 2011-2012 operating period, in conjunction with the planned T pulse schedule providing fueling of 4 g T injected per day. Whilst initial assessments have been carried out, this contribution will bring together the post-mortem analysis results and fuel injection data available from 2015-2016 operations to update the retention fraction in PFCs and use this to predict T accumulation and retention based on fueling data from T operations, currently ongoing at JET. The T assessment is applicable for a number of aspects related to JET operations and experiments. Inventory assessment for design and operation of future in-vessel laser induced desorption diagnostic: A Laser Induced Desorption – Quadrupole Mass Spectrometry (LID-QMS) diagnostic to measure in-vessel tritium accumulation is being designed for future installation and operation in JET. A first assessment of predicted retention and accumulating T inventory has been used to inform the diagnostic design in terms of laser pulse frequency, laser spot size and mirror scanning motors parameters and demonstrated how frequently significant changes in fuel accumulation may be measured. For example the areal concentration of T at the top of the inboard target tile will be 1.0e17 T atoms/cm² after four days of T operation. This requires an area ~5 cm² to be rastered in ~0.5 s to release sufficient fuel, 5e17 T atoms, and overcome pumping in order to achieve detection by QMS, located in a pumped duct outside of the main vacuum vessel. This rastering requirement can be achieved with a 3 mm diameter laser spot at frequencies up to 150 Hz. Accumulation of tritium inventory: An ongoing assessment of first wall retention inventory will provide data for tritium accounting in conjunction with T fueling data and gas recovery in the JET Active Gas Handling System. Total inventory following tritium operations: Based on the anticipated pulse schedule, an evaluation of the T inventory in PFCs and associated deposition will inform T clean-up experiments planned at the end of JET T operations. The results may also be used to aid in the assessment of waste liability.