Married filing jointly is one of the more sexist things codified in US law. It basically says women make no money and the man has to provide for everyone with a big salary so deductions and credits for the big earner. Or it says that if you're a dual income bunch of shmucks, that your wife must make 80% of what you do.
Think about when these laws were written and look at it through a historical context. Once you do, it will outrage even the most even keeled.
Since some people are downvoting for bad reasons, I'll just toss in this anecdote:
My parents were audited by the IRS for 5 years straight. They were convinced that my father "was hiding income through losses in your wife's business." My father was a surgeon; my mom ran an antiques shop. The IRS auditors setup camp in our living room for a month going on five years. That quote was straight from the lead auditor's mouth. I remember it very starkly as a young teenager. (I said hi to them each morning on my way to and from school) It really peeved me that they viewed my mom (the woman) as a failure and only a place for my father (the man) to "hide income."
Every year they came to the same results. My mom's bookkeeping was a mess, but she always overpaid her taxes and we got a refund at the end of the audit. The best kicker? My mom made more than my dad. The IRS thinks women should make less than men (by word and by audit).
As for the historic reasons of this thinking, see my reply below.
If married filing jointly isn't sexist, why are the income brackets different? Even for married filing separately, why are they different than for single people? Sit and think about it for a minute.
Sure. When the federal income tax was instituted in 1913, all of the tax rates were individual (and the lowest bracket covered most Americans). People who were married could lump sum their income and divide by 2 to find the correct rate. Married filing jointly back then was just a way to save on paperwork and hassle. Lump the two incomes together, divide by two, and treat the two people equally. That was it.
In 1948, you got the official married filing jointly "status" and with it, the various income credits, deductions, etc. One would think that the married filing jointly tax rates would simply be double what the individual rates were, right? Wrong. The joint rates were about 1.8x the individual rates. Someone was 100%, someone was 80%. This being 1948, the woman in the dual income family was 80%. The IRS didn't want to appear to favor married couples over single people (even though they did), so they said 1.8X instead of 2X the individual rates. If you were lucky enough to be a big wage earning white male in 1948 America, you got a huge tax break since stay-at-home moms were the norm, there was a baby boom going on, and only about 20-25% of women worked.
Married filing jointly is silly. It should be a sum of the family income, divided by two, then mapped to the individual rates.
> One would think that the married filing jointly tax rates would simply be double what the individual rates were, right?
Certainly not, why would I expect that? That's mean that if there's a family of two paying individual rates, they pay X% of the income, but if they file MFJ, they pay 2X% of the same income, or twice as much. How would it make sense?
> The joint rates were about 1.8x the individual rates.
Do you mean the tax brackets and not rates?
> Someone was 100%, someone was 80%.
That is a weird conclusion - why not each one 90%, or one 110% and one 80%, or one 180% and one 0%? Having MFJ rate does not imply any distribution of income, not that I can see it at least.
> This being 1948, the woman in the dual income family was 80%
What you mean "was"? Do you mean average married woman's income was 80% of average man's income in 1948? Maybe (I have no idea, didn't check) but what this has to do with tax rates? If it was so, it was certainly not because of the tax rates.
> Married filing jointly is silly
No it's not. The fact is our society is organized around families. It's not everybody, but mostly that is how it works (and MFJ is optional of course, so if you don't like the model, you can stay away from it). Taxing family - or household - as one unit makes a lot of sense, because that's how the actual households commonly work, the income and the expenses are shared. Just as taxing a company as a unit makes sense, instead of taxing each employee's production individually, so does it make sense for a household.
> It should be a sum of the family income, divided by two, then mapped to the individual rates.
That's another question. Maybe specific tax brackets need to be adjusted, maybe not - at least this link suggests that MFJ has actually lower brackets (and thus higher taxes) than two individual incomes: https://en.wikipedia.org/wiki/Marriage_penalty
But: all that explanation failed to show where does it say "women make no money". It is true that in 1948 a lot of women did not make any money as employees, and instead were providing services to their families which weren't remunerated monetarily, but I see how having (optionally) the household as taxpaying unit implies "women make no money". It still makes no sense to me.
Think about when these laws were written and look at it through a historical context. Once you do, it will outrage even the most even keeled.