Medicare beneficiaries signing up for prescription drug coverage (Medicare Part D) now through Dec. 31 have a new Web tool to help them compare plans and costs. Called Plan Finder, the Medicare site lists premiums, co-pays and deductibles by state.

Weighing all three costs is important, says Stuart Guterman, director of the Program on Medicare’s Future at the Commonwealth Fund, a nonprofit advocacy group. Some plans may have premiums as low as $25 per month and no deductible, but high co-pays.

Co-pays vary with the category, or tier, to which your drug is assigned. Guterman advises making a list of your drugs, then checking any plan you’re considering for tier and cost. Compare totals before signing up.

Under Medicare regulations, insurers can’t change tier prices before 2009 but can move drugs from tier to tier.

But according to the Medicare Rights Center in New York, if you’re on the drug before its tier changes, you can continue paying the cheaper price. Hassles? Call Medicare at (800) 633-4227.