The deadline to file federal income tax returns is April 15, just days away. But the IRS says about 40 percent of Americans haven't filed yet. Many, including small business owners, are requesting more time.

Environmental consultant Wayne DeFeo has plenty of projects to think about as he drives to meetings with clients. But these days, he's forced to consider something much less pleasant: his taxes.

"Every year is a challenge, but this year it's more of a challenge because of the unknown. You don't know what to do, what to expect," he said.

Small business owners like DeFeo are struggling to understand the changes in last year's tax overhaul. The IRS estimates nearly 8 million LLCs will request extensions this year, along with a record 14.6 million individuals. The confusion around the new law means DeFeo will join them.

"I don't think i'll be happier but I hope i'm better. I hope so. I don't know," he said.

The new tax law changes make calculating deductions this year more difficult. For example, who may qualify for business tax cuts and how much they can deduct. That is still open to interpretation.

"We're telling our clients, you know, to the extent they can, to go on extension," said accountant Joe Perry.

The situation is not only difficult for people like DeFeo, but for accountants like Perry, of the firm Marcum.

"There are certain instances where we did get guidance. But the guidance is 200 pages and when you sift through that guidance, it leads to more questions," Perry said.

DeFeo won't get his answers until after he files, which now won't be until October.

"I don't know if it's going to impact my cash flow the way I have to put more money aside for this year because i'm not sure. I may even do better, I don't know," he said.