I've a curious question. Hypothetically, if you made 50k in 2016 in the stock market but didn't do your taxes that year and then loss 50k in 2017. Would the capital losses you report in 2017 offset the taxes you've to pay in 2016 or does it not work in backwards fashion?
Definitely not and you'd be hearing from the IRS on why one didn't file in 2017 for the 2016 gains which would usually not result in a refund. The only thing that allows for this type of back filing of losses are 1256 contracts (futures) but it wouldn't allow for one to coalesce filing of 2 years into 1. They still have to be done in succession.
Yup. What he said. A friend of mine got caught up in this. A few years back he was shorting financials. He made some big bets against Bear and Lehman, and made a small fortune in 2008, but didn't pay his taxes right away, thinking that he would deal with it in 1Q2009. In that time, he made a huge bet that Morgan Stanley would go belly-up, and lost it all--including the money he owed in taxes. He busted, owing the IRS a ton of money. After many nasty letters, meetings, and hassles, and it took him years to pay it off working a full-time (non-trading) job. Basically, by not paying his 2008 taxes, he was playing the market with IRS money. Also note that you can't "settle" with the IRS. If his debt was to a creditor, credit card, mortgage lender, etc., they might be willing to negotiate a settlement amount. Not so with Uncle Sam; he can afford to wait. Every cent will be paid, unless you die.
Many settle or negotiate a lessor payment with the IRS unless they write something or say something to psssst them off. https://www.irs.gov/individuals/offer-in-compromise-1 I have a friend in the U.S. (futures trader) that owed 40k in taxes from his profits...money gone to pay for debts due to medical bills associated with his wife illness (she needed surgery). IRS verified his situation and they settle the 40k down to 8k because that was all he had left. They even recommended he get a job with dental/medical benefits considering he got into financial trouble because he didn't have private insurance...his fault because he didn't treat his trading like a business. I've even heard of famous celebrities owning a ton of money (in the millions) and they remain stubborn...refusing to pay even after the IRS was willing to negotiate a lower payment like knocking off a few hundred thousand. They ended up in court or eventually going to jail (prison) or having property (mansions) seized by the government.