published Jan 9th 2017, 3:00 am, by Ben Steverman

(Bloomberg) —
It’s tax time again, and President-elect Donald Trump and his fellow Republicans in Congress have promised to slash them—especially for corporations and the rich.

For millions of Americans, however, a tax increase will be the first thing they see. About 12 million workers will pay more this year because of an automatic adjustment in their payroll taxes. Unlike previous years, this rise in the Social Security “taxable minimum”—the amount of income subject to tax—is a whopper: 7.3 percent, the most in 34 years. That could cost each affected worker as much as $539, and much more if they’re self-employed.

Why is 2017’s increase so huge? And where does this taxable minimum come from, anyway? Let us explain. What’s changing this year?

Workers at the top of the income spectrum pay Social Security payroll taxes only on a portion of their wages. For the past two years, only the first $118,500 of earnings was subject to the 6.2 percent tax. In 2017, this taxable minimum jumps to $127,200.

How much could this cost me?

If you make less than $118,500, you won’t notice a difference. But if you earn more, an extra $8,700 could now be subject to the 6.2 percent Social Security payroll tax, costing you as much as $539 more by the end of the year. Employers, who pay their own 6.2 percent tax on payrolls, will see costs rise, too—self-employed workers could see their Social Security tax burden jump to more than $1,000. As always, however, they’re able to deduct the employer portion on their income tax returns.

What’s the total price tag to U.S. households?

About $11.6 billion in new tax revenue could come from the change in 2017, the Social Security Administration estimates.

Why such a big increase?

A 7.3 percent hike is way above inflation: The main U.S. consumer price index was up 1.7 percent in the 12 months ended in November (the latest data available), and it rose just 0.7 percent in all of 2015. So what’s going on here? Well, the Social Security taxable minimum is adjusted annually based on an index of U.S. wages, not consumer prices. The National Average Wage Index was up 3.5 percent in 2015, five times faster than inflation.

But the real reason for this sudden, steep hike is simply that the government is making up for lost time. The 2017 hike is essentially two years of wage gains packed into one. The wage index also rose 3.6 percent in 2014, but the Social Security Administration couldn’t raise the taxable minimum last year because rules prevent an increase from happening in a year when Social Security recipients don’t get a cost-of-living increase.

How unusual is a 7.3 percent increase?

It’s the largest percentage rise since 1983. When the Social Security tax began in 1937, it applied only to the first $3,000 earned, an amount that remained steady until 1951. Congress then periodically raised the taxable minimum until laws in the late 1970s began indexing it to wage growth.

Adjusted for inflation, the rise in the taxable minimum looks less dramatic. You can still, however, see the impact of substantial rises in the 1960s and 1970s, which helped pay for Social Security benefit increases for middle-class and upper-middle-class Americans.

How many people are affected?

About 12 million will pay more because of the higher minimum this year, the SSA estimates, out of 173 million workers paying into Social Security. In any given year, about 6 percent of all workers make more than the taxable minimum, a number that’s been consistent for decades. The SSA estimates that almost 20 percent of workers reach the taxable minimum at some point in their careers, even if it’s only for one year.

Why does the taxable minimum exist?

The U.S. income tax was envisioned as a progressive tax, with the wealthiest supposedly bearing the largest tax burden and the lowest-income Americans paying nothing or even receiving tax credits. The Social Security payroll tax is unusual in that lower-income Americans end up paying a greater share of their income than the rich.

The main idea is that the Social Security taxes you pay should more or less correspond with the benefits you eventually receive. The benefit formula is progressive, however, with lower- and middle-income workers getting bigger Social Security checks relative to what they put in than the wealthy. No matter how much you contribute, the most you can get from Social Security this year is $2,687 per month.

Doesn’t Social Security need money?

In the course of the 2016 election campaign, an increasing number of Democratic politicians and policy experts floated the idea of raising more revenue for Social Security. The idea was to use the money to expand benefits and patch the program’s long-term funding shortfall. Those ideas are largely dead under a Republican-controlled White House and Congress.

One argument for raising the taxable minimum is that the Social Security payroll tax hasn’t kept up with massive, ever-widening income inequality in America. While the share of citizens who exceed the taxable minimum has held steady, the share of the nation’s income subject to the Social Security payroll tax has been slipping, from 90 percent in the early 1980s to less than 83 percent. That’s because workers at the very top are earning so much more than they used to, and the vast majority of their wages avoid Social Security payroll taxes.

Does the rate hike mean my benefits will rise, too?

Barely. While the taxable minimum is based on an index of U.S. wages, Social Security benefits are based on prices. Given low inflation, they’re inching up just 0.3 percent. That 2017 cost-of-living adjustment means the average retired worker gets an extra $5 a month, bringing the average retiree’s monthly Social Security check to $1,360.

Any other nasty surprises coming in 2017?

If you try to max out your retirement accounts every year, you may be disappointed to learn that the amounts you can contribute to an individual retirement account or a 401(k)-style retirement plan are holding steady. In 2017, there’s still an annual limit of $18,000 for contributions to a 401(k) and $5,500 for an IRA. Workers 50 and older can save an extra $6,000 in a 401(k) and $1,000 in an IRA, so-called catch-up contributions that are also the same as last year.

One change in 2017 that could be very costly to some Americans relates to tax refunds. A new law requires the Internal Revenue Service to hold onto refunds for people claiming the earned income or additional child tax credits until mid-February. The IRS also warned that new safeguards against fraud and identity theft could delay refunds further.

A delayed refund isn’t technically a tax increase. But it might feel like one for millions of low-income Americans who typically rely on refunds to pay back debt and cover basic expenses at the beginning of the year.

–With assistance from Jordan Yadoo in Washington