Negative income tax as in universal payment, no formal personal allowance, flat tax rate, and the interaction between them creating an effective personal allowance.
Is a spreadsheet example I did years ago.
https://docs.google.com/spreadsheet...j2E2rjulugi6MMLUvpB0QiRJ92E/edit?usp=drivesdk
It ensures that the impact of any tax or benefit change voted for by the public can't be used to punish people, due to equal treatment. You can also add in additional variables such as disability or child enhancements by adding them to the payment amount which again serve to give more money, either in the form of a larger net payment or a larger effective personal allowance.
Simple, easy to administer, consistent and fair.