Hi, I can help you with your question.
Paying the full (20% less) amount in 2011 would provide you a savings of $2,523.60, without considering the medical expense tax deduction.
Alternatively, using a payment plan to pay the full $12,618 would allow for a 20% greater deduction on the combined tax returns for the years in which the plan covers. Please note, however, the deduction is only available for taxpayers who itemize their deductions. The increased deduction would then only provide a percentage (35% or less) of the $2,523.60 mentioned above.
Assuming funds are available, paying the full (80% less) amount in 2011 would provide the most savings.