Brace yourself for the next financial whammy:

It’s open enrollment season for workplace health insurance plans — and many of the 158 million Americans who receive employer-based health insurance can expect to pay more of the costs.

About two-fifths of U.S. firms do not offer employee health benefits. And even at those that do, many health-benefits packages will be a “skimpier and less comprehensive,” said Drew Altman, chief executive of the Henry J. Kaiser Family Foundation.

Kaiser, together with the Health Research & Educational Trust, recently released a 2008 snapshot and 2009 outlook for employee health benefits.

Cost increases for 2009 actually continue a modest cost-containment trend of the last three years — an improvement over double-digit cost increases before 2005.

But the real long-term effect on employers and employees is that premium costs have more than doubled since 1999.

In 1999, total family premiums for employer-sponsored health insurance averaged $5,790, of which workers paid an average of $1,543, according to Kaiser.

This year, premiums for such coverage rose to $12,679, with employees paying an average of $3,354 out of their paychecks to cover their share of the costs, the Kaiser report said.

In 2009 — provided you’re fortunate enough to work where an employer-sponsored plan is offered — you could be asked to pay a bigger share of the premium cost, a higher deductible amount and more out-of-pocket expenses for prescription drug costs and office visit co-pays.

Exactly how much more workers will pay next year will vary widely.

Nationally, cost increases for employers who offer health insurance plans will average between 8 percent and 10 percent, a Mercer survey indicates. A Towers Perrin survey puts the employers’ cost increase as low as 6 percent.

But employers have said in several surveys that they do not intend to shoulder their increases alone.

David Power, with Power Benefits Group, says about one-third of his employer clients in the Kansas City area are saying they cannot afford to live with the cost increases they’re getting from their carriers in this enrollment season.

“But their last resort is to walk away from providing employee health insurance,” Power said. “Employers who provide health benefits want to keep them as a recruiting and retention tool.”

Power says employers are responding to cost increases, in this order:

“The first response is to negotiate with the carrier and try to find the reason for the cost increase. The second response is to look at the plan design and try to mitigate what the company pays, usually by asking employees to pay more out of pocket. The third response is to shop the plan.”

Shopping the plan — trying to find another carrier for less money — is being done fairly reluctantly, area brokers said. It causes disruption in health-care providers for employees, plus time and burdensome paperwork.

The most common response is to shift a larger share of premium costs to employees. Area brokers said a growing number of plan deductibles will exceed $1,000, with some getting kicked up as high as $2,000.

Some co-pay costs for office visits are rising, too. And some employers are shuffling their benefits packages in other ways.

For example, Jim Wolf, senior sales representative for Assurant Employee Benefits, says some employers will continue to offer group dental plans, but only if the employee opts to pay 100 percent of the costs.

“That still may be a better deal than the employee could find individually on the open market,” Wolf said. “And there’s also an access question. With a group plan, the employee is guaranteed access, where he might be refused individually.”

Employers that have self-funded insurance plans might be better able to mitigate cost increases by redesigning or re-insuring their plans.