Business Insider reports the last day to file your 2018 tax return is Monday, April 15. It's the first tax season under the new tax law President Donald Trump enacted in late 2017. It's also the most significant overhaul of the US tax code in 30 years. But if you receive a smaller refund or owe money to the IRS, financial experts say it doesn't mean you're worse off financially. It just means the boost in your paycheck when the law took place already took care of the "refund" all along.