I don't know UK tax law, but there is public healthcare. So one major deduction in the US is completely moot in the UK. The IRS doesn't know what your healthcare expenses were for the year. There are a half dozen similar scenarios. Yes, a lot more could be automated, but it's also the case that too much automation would wrongly automated people out of their money. It would make sense to mail people a prefilled sheet that says, "here's what we know about. Review and make sure you check x, y, z, etc., to see if it's applicable."