We have some of these in the UK tax system, some of which are being resolved (or at least improved) but many which aren't. Currently, if you have a child, you'

We have some of these in the UK tax system, some of which are being resolved (or at least improved) but many which aren't. Currently, if you have a child, you're entitled to a cash payment called child benefit. For a first child it's worth £26 per week and then any subsequent children you'd get £15.90 per week. However, you only get this if the highest earner's income is below £50,000. Between £50k and £60k, it's on a sliding scale, so at £55k you get 50%, £57.5k you get 25%, etc. Side effects of this are that if you have two earners both on £49999, you get the full amount, and one earner on £60000 you get nothing. It means there's a crazily high effective marginal rate on people. If you put money into your pension, it can bring you down below the threshold again, so many people (if they can afford to) will do this. From next month, they're changing the threshold to £60-80k over which it drops off, which is a big improvement, but the marginal tax rate effect is still there.