My MacBook Air's battery health is decreasing.

Question

My Macbook Air's battery health is decreasing. I bought it around a year ago. Now it's battery health is 85%. However, it keeps changing. From 85% to 88% and sometimes it hit 90%. Is my macbook's battery healthy? And is it normal, because I bought it a year ago.
Here are my battery's properties:
Cycles     ; 404
Health     : 85%
Design Capacity: 6700 mAh
Current Capacity: 5703 mAh

Answer 1

i have to disagree with linc davis's reply.
system profiler, or what they call the system report will have your current battery health status. in power the system profiler will either display "excellent", "normal" or "check battery" the more charge cycles you have, (404 which you stated) the more the battery will loose some capacity. this is normal of lithium ion batteries
health 85 % is current capactiy (fully charged)  divided by design capacity * 100 or
5703 / 6700 *100 = 85%
my mac book air, having it for a year states
cycle count 163
Condition : Normal
Charge remaining 4223
full charge capacity 4263
but system profiler, at least on my mac book air running osx 10.8.2 does not list design capacity. so i am wondering where you got that number. the mac book air i have is the mid 2011 11" model
if you feel after 400 cycles your battery diminished and you have apple care you can always ask them to replace the battery, but if you did not get apple care, then the year warranty would be up. a new mac book air battery outside of apple care or any warranties is $129 before tax at the apple store.
eventually the more cycles you have ( a cycle is being fully charged from being nearly discharged ) the more you are going to have to replace the battery. whenever you feel you are not getting the charge you used to get the discision to repalce that battery is your choice, but eventually you will have to replace it.
for example say the battery used to give you 3 hours amd now it only gives you 30 minutes, then yeah replace the battery. but if the time lost in capacity doesn't bother you that much, then don't replace the battery now