Do you have to grant a total month of coverage if anly a partial month's payment is recieved? Our feeling is that you do, but we would welcome additional comments. Thanks in advance for your help!

How much was it underpaid?

54.4980B-8 Q-5 (d)

(d) If timely payment is made to the plan in an amount that is not
significantly less than the amount the plan requires to be paid for a
period of coverage, then the amount paid is deemed to satisfy the plan's
requirement for the amount that must be paid, unless the plan notifies
the qualified beneficiary of the amount of the deficiency and grants a
reasonable period of time for payment of the deficiency to be made. For
this purpose, as a safe harbor, 30 days after the date the notice is
provided is deemed to be a reasonable period of time. An amount is not
significantly less than the amount the plan requires to be paid for a
period of coverage if and only if the shortfall is no greater than the
lesser of the following two amounts:
(1) Fifty dollars (or such other amount as the Commissioner may
provide in a revenue ruling, notice, or other guidance published in the
Internal Revenue Bulletin (see Sec. 601.601(d)(2)(ii) of this
chapter)); or
(2) 10 percent of the amount the plan requires to be paid.