S.2621 - Federal Government - A bill to amend the Terrorism Risk Insurance Act of 2002, to temporarily reduce the insurer deductibles for insurers sustaining insured losses from large terrorism events.

Terrorism Risk Insurance Improvement Act of 2008 - Amends the Terrorism Risk Insurance Act of 2002 to revise the definition of "insurer deductible" with respect to a situation where aggregate industry insured losses resulting from a certified act of terrorism exceed $1 billion for an insurer that sustains any of such losses.

Sets forth a calculation for the value of such an insurer's direct earned premiums over the calendar year immediately preceding the program year.