It depends on how you have been keeping your seeds. Seeds have to be protected from changes in temperature and moisture in storage. They can be stored in the freezer or refrigerator. The colder the better for longer life.
With a few exceptions corn and zucchini, most seeds are good for 3-5 years if they are properly stored. Some seeds like dill, beans, fennel will still germinate up to 10 years later.
Three year old seed may have a lower germination rate. I have planted basil up to five years later, but I do keep mine in cold storage in the frig. I also put down more seed if the seeds are older to offset the poorer germination rate. You can try germinating 10 seeds in a moist paper towel. The number of seeds that germinate x 10 will be your approximate germination rate.
With seeds that are old I put more seeds than usual in the pot, The soil mix should be moist before you plant. Basil seeds cannot be soaked before. They will puff up, that is why they are hard to sterilize against seed borne disease. I put a paper towel on top of the pot and water through the paper towel until the seedlings pop up. I will start checking under the paper towel starting around 7-10 days. If they don't show up after 3 weeks, then the seeds are probably too old and you need to start with new ones.
https://extension.oregonstate.edu/garden ... seeds-last
https://theherbgardener.blogspot.com/201 ... herbs.html