Stock you've purchased, you own, regardless of whether you stay with the company with that ticker symbol. The picture is more complex when dealing with stock options and grants, however. In these two cases, you've got the potential to a nice bump in your compensation package, but your vesting schedule dictates what stock, if any, you own or can buy.
Employee Stock Purchase Plan
An employee stock purchase plan allows you to set aside a percentage of your salary toward purchasing the company's stock. You buy the stock at a discount, typically 15 percent less than the price of the stock at the open or close of the buying period, whichever price is lower. You also don't typically pay any fees or commissions to purchase it. Once you've bought the stock, it's your property. When you leave, you can transfer it to your own investment account or sell it. Any funds deducted from your paycheck, but not yet used to purchase stock, are refunded to you. You may have a limited amount of time to buy stock through the plan after leaving your job, so make sure to research this quickly if you think you're interested in making such a purchase.
Stock options give you the right to purchase stock at a set price, called the strike price. If the stock is doing well, the price can be significantly lower than the trading price for the stock. You don't own this stock, however. You own the right to buy the stock at the strike price. And, you don't necessarily own all the rights. Typically, you vest into your options over a five-year period. If you leave after two years, you only have rights to 40 percent of your vested options, for example. Your unvested options are not available to you -- you forfeit the rights to them upon termination. When you terminate your employment with the company, you must exercise those options within a specified time after you leave, typically 60 days. Once you exercise your options, you own the stock free and clear, regardless of your employment status with the company.
Stock grants operate both with and without vesting schedules. When you receive a stock grant that doesn't require vesting, you don't have to buy the stock, you own it. This type of compensation clouds your tax picture, since you have to pay tax on the value of the stock received, but it doesn't cloud your investment portfolio. If the stock grant uses a vesting schedule, then you own any shares (and pay taxes on those shares) as you vest into them. In addition, when you quit, you forfeit your right to shares in the stock grant into which you haven't vested.
Keeping It All Straight
To keep track of what's going on with your calendar and stock, create a simple spreadsheet. Track which shares you buy, the price at the opening of the period and the price at the close. When the period ends, enter the price at which you bought the stock as well the number of shares. For any vesting options, identify the strike price for the option, the number of shares into which you vest and when. For a stock grant, record the value of the shares and any vesting schedule. Keeping track helps prepare for the income tax issues that arise if you eventually sell the stock.