I was wondering how often all of you replace your baking soda/powder? I've read in one of my cookbooks that they should be replaced every 6 months. I barely go through either of them when I purchase them before I do most of the cookie baking around Thanksgiving/Christmas time. Of course it's not that expensive to buy a new package of baking soda/powder every 6 months or even once a year. Just curious if all of you replace yours that often, of if you find that the levenings still work up to a year or longer after opening?
I use baking soda pretty quickly because I also use it for cleaning and for freshening the laundry, so it goes really quick. I buy seperately for those chores, but always seem to use up all I have. Baking powder, I probably buy every 6 mos. I bake healthy muffins for DH to carry to work for breakfast, since he does not eat at home before work. I use baking powder and soda in those as well, so I use it up more quickly. I have been know to throw out a can of baking powder to buy a new one if I've got something special to bake, just to make sure it's fresh.
I use my baking powder quicker than the soda. I made a lot of pancakes from scratch and biscuits.
I always buy Clabber Girl brand baking powder and it has a date stamped on the bottom of the can. If it's past that date, I throw it out and buy a new one. I usually buy new baking soda every 3 months or so....if I still have some left in the old container, I use it to scour my sinks or bathtubs with or throw it in the fridge to absorb odors. It's so cheap that it's not really a big deal to replace it that often, IMO. There's a test you can do for both baking soda and powder, though, to see if it's still good or 'active'...wish I could remember what it was! 
Here's a link that talks about baking powder and baking soda. It says baking soda has an indefinite shelf life and gives the way to test baking powder and baking soda to see if it's still active:
http://joyofbaking.com/bakingsoda.html
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