If you are trying to plan for storage allocation, plan for the worst case scenario and hope you don't have to deal with it. Worst case scenario is that it detects an issue and needs to download the full game again, which means about 30-40GB. On PS, that means it will also need 30-40GB to decompress and do the installation before it cleans up all the install files - so 60-80GB. If it does the proper incremental update then likely around 5ish GB as noted by Dragon. Only PS seems to have big issues with the incremental updates however.