Short or Long Term Capital Gains for Multiple Investments
The default is FIFO: first in - first out. Unless you specifically instruct the brokerage otherwise, they'll report that the lot you've sold is of Jan 5, 2011. Note, that before 2011, they didn't have to report the cost basis to the IRS, and it would be up to you to calculate the cost basis at tax time, but that has been changed in 2011 and you need to make sure you've instructed the brokerage which lot exactly you're selling. I'm assuming you're in the US, in other places laws may be different. Tell your broker.  You can usually opt to have certain positions be FIFO and others LIFO.  Definitely possible with Interactive Brokers.
You need to report the income from any work as income, regardless of if you invest it, spend it, or put it in your mattress (ignoring tax advantaged accounts like 401ks).  You then also need to report any realized gains or losses from non-tax advantaged accounts, as well as any dividends received.  Gains and losses are realized when you actually sell, and is the difference between the price you bought for, and the price you sold for.  Gains are taxed at the capital gains rate, either short-term or long-term depending on how long you owned the stock.   The tax system is complex, and these are just the general rules.  There are lots of complications and special situations, some things are different depending on how much you make, etc.  The IRS has all of the forms and rules online.  You might also consider having a professional do you taxes the first time, just to ensure that they are done correctly.  You can then use that as an example in future years. The main reason to exercise the shares sooner rather than later is that you have to hold the shares for 1 year to gain access to the long-term capital gains rate when you sell your shares. You do not want short-term capital gains rates to apply to these shares when you sell them. If the company is unable to go public and sells privately, you may not have any choice but to sell your shares immediately. If the company goes public you will simply have to hold your shares for a year after you buy them before selling to get the lower tax rate. "Appreciation of a Capital Asset is a Capital Gain.   In the United States, Capital Gains get favorable tax treatment after being held for 12 months. From the IRS newsroom: Capital gains and losses are   classified as long-term or short-term,   depending on how long you hold the   property before you sell it. If you   hold it more than one year, your   capital gain or loss is long-term. If   you hold it one year or less, your   capital gain or loss is short-term. The tax rates that apply to net   capital gain are generally lower than   the tax rates that apply to other   income. For 2009, the maximum capital   gains rate for most people is15%. For   lower-income individuals, the rate may   be 0% on some or all of the net   capital gain. Special types of net   capital gain can be taxed at 25% or   28%. The IRS defines a Capital Asset as ""most property you own"" with a list of exclusions found in Schedule D Instructions.  None of the exclusions listed relate to Bond ETFs." Capital gains tax is an income tax upon your profit from selling investments. Long-term capital gains (investments you have held for more than a year) are taxed significantly less than short-term gains. It doesn't limit how many shares you can sell; it does discourage selling them too quickly after buying.  You can balance losses against gains to reduce the tax due. You can look for tax-advantaged investments (the obvious one being a 401k plan, IRA, or equivalent, though those generally require leaving the money invested until retirement). But in the US, most investments other than the house you are living in (which some of us argue isn't really an investment) are subject to capital gains tax, period. Here's how capital gains are totaled: Long and Short Term. Capital gains and losses are either long-term or   short-term. It depends on how long the taxpayer holds the property. If   the taxpayer holds it for one year or less, the gain or loss is   short-term. Net Capital Gain.  If a taxpayer’s long-term gains are more than their   long-term losses, the difference between the two is a net long-term   capital gain. If the net long-term capital gain is more than the net   short-term capital loss, the taxpayer has a net capital gain. So your net long-term gains (from all investments, through all brokers) are offset by any net short-term loss.  Short term gains are taxed separately at a higher rate. I'm trying to avoid realizing a long term capital gain, but at the same time trade the stock. If you close in the next year, one of two things will happen - either the stock will go down, and you'll have short-term gains on the short, or the stock will go up, and you'll have short-term losses on the short that will offset the gains on the stock.  So I don;t see how it reduces your tax liability.  At best it defers it. My friend Harry Sit wrote an excellent article No Tax Advantage In RSU.  The punchline is this. The day the RSUs vested, it's pretty much you got $XXX in taxable income and then bought the stock at the price at that moment. The clock for long term gain starts the same as if I bought the stock that day.  Historical side note - In the insane days of the Dotcom bubble, people found they got RSUs vested and worth, say, $1M. Crash. The shares are worth $100K. The $1M was ordinary income, the basis was $1M and the $900K loss could offset cap gains, not ordinary income above $3000/yr. Let me be clear - the tax bill was $250K+ but the poor taxpayer had $100K in stock to sell to pay that bill. Ooops. This is the origin of the 'sell the day it vests' advice.  The shares you own will be long term for capital gain a year after vesting. After the year, be sure to sell those particular shares and you're all set. No different than anyone selling the LT shares of stock when owning multiple lots. But. Don't let the tax tail wag the investing dog. If you feel it's time to sell, you can easily lose the tax savings while watching the stock fall waiting for the clock to tick to one year. Firstly 795 is not even. Secondly - generally you would pay tax on the sale of the 122 shares, whether you buy them back or not, even one minute later, has nothing to do with it. The only reason this would not create a capital gains event is if your country (which you haven't specified) has some odd rules or laws about this that I, and most others, have never heard of before. "1) When it says ""an investment or mutual fund"", is a mutual fund not   an investment? If no, what is the definition of an investment? A mutual fund is indeed an investment. The article probably mentions  mutual funds separately from other investments because it is not uncommon for mutual funds to give you the option to automatically reinvest dividends and capital gains.    2) When it says ""In terms of stocks"", why does it only mention   distribution of dividends but not distribution of capital gains? Since distributions are received as cash deposits they can be used to buy more of the stock. Capital gains, on the other hand, occur when an asset increases in value. These gains are realized when the asset is sold. In the case of stocks, reinvestment of capital gains doesn't make much sense since buying more stock after selling it to realize capital gains results in you owning as much stock as you had before you realized the gains. 3) When it says ""In terms of mutual funds"", it says about ""the   reinvestment of distributions and dividends"". Does ""distributions"" not   include distributions of ""dividends""? why does it mention   ""distributions"" parallel to ""dividends""? Used in this setting, dividend and distribution are synonymous, which is highlighted by the way they are used in parallel. 4) Does reinvestment only apply to interest or dividends, but not to   capital gain? Reinvestment only applies to dividends in the case of stocks. Mutual funds must distribute capital gains to shareholders, making these distributions essentially cash dividends, usually as a special end of year distribution. If you've requested automatic reinvestment, the fund will buy more shares with these capital gain distributions as well."