Sugru will stay fresh for 13 months from the date it was made. If you use it within its date, the cured Sugru will last and last (and last and last and last). You'll find a Use By date on the back of each individual single use foil pack.
However, if you'd like your Sugru to last longer than 13 months, we've got a pro tip for you. You can triple the shelf-life of Sugru by keeping it in the fridge - especially helpful if you live in a warm climate! (Just so you know, the maximum recommended storage temperature is 21°C/70°F).