Who decided what day tax time was and what was the reason?

Banks, brokers, and most other businesses run on a January-December fiscal year. It takes them a certain amount of time to ‘close the books’ and get all of the previous year’s numbers ready for distribution to customers. It used to take much longer (pre-computers) but now their deadlines are usually at the end of January.

I think that the theory was that citizens would get their W2 and 1099s and other previous-year documentation by late January, and they had a couple months to get their tax info compiled and submitted.

So as I understand it, it’s basically an outgrowth of the fiscal year calendar.

In the US it used to be March 15th for personal tax returns, but in the 1950’s it was changed to April 15th. Actually, I think military were given until April 15th even before the change for everyone else.

It’s decided by the government, I think congress passes tax laws and the IRS is the administrator. There have been tax lawsuits in US history that have gone to the Supreme Court arguing a tax is unconstitutional.