“$168 billion”

-- The estimated cost of compliance to American taxpayers in 2010, including tax preparation fees, hours worked and other costs, according to the IRS.

It’s D-Day for President Obama’s health law as millions of American tax filers face the deadline for reporting their status under Obama’s new entitlement program and their vulnerability to new taxes used to fund it.

Americans have been paying the biggest new taxes associated with the law since the beginning of the year: a .9 percent income tax and a 3.8 percent tax on investment income, both for top earners.

While the estimated cost of those taxes is $318 billon over the next decade, like this year’s other big tax hike, the 48 percent jump in the payroll tax rate for all workers, they occur automatically and don’t create sticker shock except for those who count every penny in every paycheck.

Americans are also already living with two other costly tax increases in the law.

Those facing huge medical bills were previously able to deduct any expenses above 7.5 percent of their annual income. That’s now 10 percent. This is a relatively small number of people, mostly with serious illnesses, and the pinch won’t come until they file their taxes next year.

The other change is a new cap on health savings accounts, now set at $2,500. But consumers already got that word during the enrollment period for their health plans at the end of last year. Many will pay higher taxes, but in small sums mostly. (The point of this regulation was more to discourage cash-based purchases of medical services and products and drive people into more expensive, comprehensive insurance plans to help insurance companies cover costs under the law.)

But today is the day when the compliance curve of the president’s law really starts to get steeper.

The Supreme Court ruled last year that whatever Obama and congressional Democrats called the penalty under the law for not having insurance, it is still a tax. And one can see why, since the initial point of contact for the uninsured with the law comes through the IRS.

The government will be using the tax returns due today to decide who will receive an estimated $25 billion in new insurance subsidies next year.

Enrollment in the new entitlement program is set to begin on Oct. 1. The complex process of enrollment looks to be an even more daunting task than tax preparation. And with many states functioning differently and delays piling up, it could be a real goat rope.

But whatever comes out and whenever it goes into place, the tax returns due today will provide the initial basis for how one’s relationship with the government and health insurance functions.

Those making up to 400 percent of federal poverty levels -- $43,560 for an individual and $89,400 for a family of four in 2011, according to the Kaiser Family Foundation – will be eligible for the new benefit.

The government will know from the tax forms due today how many Americans fall into that category. The government will still be working from estimates on how many of those folks in the subsidy zone don’t have insurance, but these forms will define the universe of those who may be eligible.

Then those individuals in the subsidy zone without insurance will have to decide whether to sign up for the program or face a fine.

By Tax Day 2015 all American taxpayers will have to provide proof of insurance to the IRS, so today starts the clock for those without insurance to either comply or face the penalty -- $95 for 2014, $325 for 2015 and $695 for 2016.

The purpose of the “mandate” in Obama’s law is to start herding people into the re-regulated insurance market, and Tax Day 2013 is the start of that great health insurance cattle drive.

Chris Stirewalt is digital politics editor for Fox News, and his POWER PLAY column appears Monday-Friday on FoxNews.com. Catch Chris Live online daily at 11:30amET at http:live.foxnews.com.