Dan's answer is spot on. Based on the facts in your question I would guess you're in the 3-10% range, lower if your salary is close to market. I would add that because of the 1 year cliff, having a large equity stake makes you more likely to be let go quickly if you're valuable but not as valuable as expected to the company. I would say that's largely a good thing, but based on your risk profile you may disagree.