From a post to Baen Bar BuShips dated March 28, 2002:

Effective intercept range for counter-missiles

    Effective intercept range for CMs has been on the order of somewhere around 1,000,000 km for around 60 to 70 years as of OBS. 1,000,000 km equates to a flight time of roughly 14 seconds against a "max velocity" pre-MDM missile, which, with cycle times on CM launchers, usually gives time for no more than three CMs (from the same ship) to target each incoming missile (unless, of course, there are so few incoming that multiple CMs can be devoted to each of them from the same defensive launch, that is). With the new MDMs, maximum terminal velocity is around 243,581 KPS, which, uh, suggests that there may be just a few teeny problems with traditional missile defense doctrine. Nowadays, you get one -- count them, one -- CM shot at a missile, and it will cross the energy engagement range (roughly 250,000 km for broadside weapons used in the missile-defense role [with very low PKs] and/or about 200,000 km for point defense lasers [with high PKs]) in about 1 second flat. Laser clusters are usually used in "ganged" intercepts, concentrating the fire of multiple mounts in single threats, but in a saturation attack such as pods can generate, the "swamping" effect prevents this, which accounts for much of the increased deadliness in missile warfare.