One of the challenging features of poverty aid is to avoid creating disincentives toward achieving self-sufficiency.
... Take a hypothetical single mother of two, Jane, earning $18,000 a year. Earning an additional $1 will increase Jane's actual cash available to spend by just 12 cents.
How can this be? The effect comes about because governments at various levels give aid to the very poor, such that the extremely low earners face negative tax rates. In short, we pay some poor to work -- this is the "welfare to workfare" move of Bill Clinton's legacy. But then the law takes these benefits back from the near-poor via high marginal tax rates in a "phaseout" range. The most important of these provisions is the earned income tax credit (EITC) located in the federal income tax. This provision pays the working poor up to 40 cents on the dollar up to approximately $10,000 of earnings.
If Jane makes $10,000, the government mails her a check for $4,000. Over a certain range, Jane keeps that money. But as she starts earning more than approximately $18,000, Jane begins to lose the $4,000, at a roughly 20% rate. Add that to payroll taxes (7.65%), the regular income tax (15%, at that range), and Jane is in a rate bracket over 40%, and we are just getting started -- other federal, state and local programs and taxes pile on to the same effect.
You might be thinking that losing a benefit is not a tax. That is an understandable sentiment, but Jane will not be comforted by it. Looking just at the EITC, as Jane's earnings go over $18,000, she loses some of the dollars she is earning to "regular" taxes, and the $4,000 she was getting in assistance is disappearing. It's real, green, money that she is losing. This is the net effect that Shaviro was describing: Compare Jane earning $10,000 in the workplace to Jane earning $25,000, and the latter Jane simply has over $2500 fewer dollars to spend.
If this is all so complex, how can it affect anyone's real behavior? But what we don't know, or don't fully, can affect us. ...
Tax policy is not my strong suit but articles like these explain why the seeming "irrational" or "lazy" of low-income folks is often not that irrational. It is the system they are navigating that is irrational.