I work year around with a W2, but I also work year around and recieve a 1099. Where and how do I pay quarterly for my 1099? For the past 3 years I've been paying my 1099 taxes once a year at the same time as my W2.
You can pay your estimated taxes at the end of the year like you have been doing but you may have a penalty for not making them quarterly it depend on your balance due amount.
Here is a good article that explains who should make estimated payments and how to make them.