And more than likely, one or both have expired. Baking soda and baking powder lose their effectiveness once they've been sitting around for a long while. Typically both last anywhere from 6 months to 1 year but make sure to check the best used by date on the bottom. With expired baking soda, you can still technically use it for cleaning because it might have some potency left, but it will not be powerful enough to use in baking.