On the bottom was stamped Expiration Date 01-28-91. We did wonder how Baking Soda can expire.
Since it is at least 15 years old and is half full, it should last until about 2020! Actually I suspect it will last longer since I don't recall that it has been used recently.
Then rsc pointed out that there was another box in the pantry closet. And sure enough there was a 2 lb. box that was opened but seems nearly full.
I saw no expiration date on it although it the .73 price was stamped on the bottom. Then I saw printed in the side of the box A Pure and Natural Product for over 125 years.
A quick trip back to the kitchen to examine the other box. This box has printed on the side The Standard for Purity and Quality for over 135 years.
Thus one can conclude that box is ~ 25 years old.
The Web site says the company is 155 years old and here is an early logo.
And with this box as spare I'd say we have an additional 60 years supply and thus we are supplied until 2080! Using the 155 years old info, if they update these slogans frequently then these boxes could be even older and thus our supplies will last even longer. If it takes 20 years to use 1/2 lb. then we have ~100 years supply left.