Transformers are a critical part of the electrical infrastructure of a country. This publication, ‘A Guide to Using Total Cost of Ownership When Purchasing Distribution Transformers’, provides information on, and guidance for using, the Total Cost of Ownership (TCO) approach that is based on the IEC methodology. The TCO approach allows purchasers to capitalise the value of future losses and incorporate them into the purchasing decision process. It therefore helps to ensure that utilities and companies purchase and install cost-optimised transformers into their network. To support the guide, U4E has produced an Excel spreadsheet tool which puts the TCO equations into a user-friendly spreadsheet to facilitate the derivation of the calculation of the loss evaluation factor.