Estimated Tax on Unplanned Capital Gains
I'm assuming your talking USA. There are two ways to look. If you know you should pay on the cap gains, the best way to handle that separately from your salary is to file a quarterly tax payment.  That, I understand, is what the self-employed have to do. I'm in the situation where at some point, probably this year, the company that employs me will be bought out, and I will owe capital gains taxes on my shares gobbled up in the buy-out.  It's a cash-for-stock transaction.  So, in my case, I've just adjusted my W-4 to take advantage of the safe-harbor provision related to taxes I payed in 2016 and my salary.  The details vary depending on your situation, but in my case, I've calculated what it will take in W-4 allowances to make sure I pay 110% of my 2016 tax payment (after refund).  I'm not worrying about what the actual taxes on those shares of company stock will be, because I've met the rules for safe-harbor. Safe harbor just means that they can't penalize you for under-withholding or underpayment.  It doesn't mean I won't have to write a check on april 15. In general, you are expected to pay all the money you owe in taxes by the end of the tax year, or you may have to pay a penalty. But you don't have to pay a penalty if: The amount you owe (i.e. total tax due minus what you paid in withholding and estimated taxes) is less than $1000. You paid at least 90% of your total tax bill. You paid at least 100% of last year's tax bill. https://www.irs.gov/taxtopics/tc306.html I think point #3 may work for you here. Suppose that last year your total tax liability was, say, $5,000. This year your tax on your regular income would be $5,500, but you have this additional capital gain that brings your total tax to $6,500. If your withholding was $5,000 -- the amount you owed last year -- than you'll owe the difference, $1,500, but you won't have to pay any penalties. If you normally get a refund every year, even a small one, then you should be fine. I'd check the numbers to be sure, of course. If you normally have to pay something every April 15, or if your income and therefore your withholding went down this year for whatever reason, then you should make an estimated payment. The IRS has a page explaining the rules in more detail: https://www.irs.gov/help-resources/tools-faqs/faqs-for-individuals/frequently-asked-tax-questions-answers/estimated-tax/large-gains-lump-sum-distributions-etc/large-gains-lump-sum-distributions-etc
Normally, you don't pay capital gains tax until you actually realize a capital gain.  However, there are some exceptions. The exception that affected Eduardo Saverin is the expatriation tax, or exit tax.  If you leave a country and are no longer a tax resident, your former country taxes you on your unrealized capital gains from the period that you were a tax resident of that country.  There are several countries that have an expatriation tax, including the United States.  Saverin left the U.S. before the Facebook IPO. Saverin was perhaps already planning on leaving the U.S. (he is originally from Brazil and has investments in Asia), so leaving before the IPO limited the amount of capital gains tax he had to pay upon his exit.  (Source: Wall Street Journal: So How Much Did He Really Save?) Another situation that might be considered an exception and affects a lot of us is capital gain distributions inside a mutual fund.  When mutual fund managers sell investments inside the fund and realize gains, they have to distribute those gains among all the mutual fund investors.  This often takes the form of additional shares of the mutual fund that you are given, and you have to pay capital gains tax on these distributions.  As a result, you can invest in a mutual fund, leave your money there and not sell, but have to pay capital gains tax anyway.  In fact, you could owe capital gains tax on the distributions even if the value of your mutual fund investment has gone down. In addition to the answer from CQM, let me answer your 'am I missing anything?' question. Then I'll talk about how your approach of simplifying this is making it both harder and easier for you. Last I'll show what my model for this would look like, but if you aren't capable of stacking this up yourself, then you REALLY shouldn't be borrowing 10,000 to try to make money on the margin. Am I missing anything? YES. You're forgetting (1) taxes, specifically income tax, and (2) sales commissions//transaction fees.  On the first: You have not considered anything in your financial model for taxes. You should include at least 25% of your expected returns going to taxes, because anything that you buy... and then sell within 12 months... is taxed as income. Not capital gains. On the second: you will incur sales commissions and/or transaction fees depending on the brokerage you are using for your plan. These tend to vary widely, but I would expect to spend at least $25 per sale. So if I were building out this model I would think that your break-even would have to at least cover: monthly interest + monthly principal payment income tax when sold commissions and broker's fees every time you sell holdings On over-simplifying: You have the right idea with thinking about both interest and principal in trying to sketch this out. But as I mentioned above, you're making this both harder and easier for yourself. You are making it harder because you are doing the math wrong. The actual payment for this loan (assuming it is a normal loan) can be found most easily with the PMT function in Excel: =PMT(rate,NPER,PV,FV)... =PMT(.003, 24, -10000, 0). That returns a monthly payment  (of principal + interest) of 432.47.  So you actually are over-calculating the payment by $14/month with your ballpark approach. However, you didn't actually have all the factors in the model to begin with, so that doesn't matter much.  You are making it artificially easier because you have not thought about the impact of repaying principal. What I mean is this--in your question you indicate:  I'm guessing the necessary profit is just the total interest on this loan = 0.30%($10000)(24) = $720 USD ? So I'll break even on this loan - if and only if - I make $720 from stocks over 24 months (so the rate of return is 720/(10000 + 720) = 6.716%). This sounds great-- all you need is a 6.716% total return across two years. But, assuming this is a normal loan and not an 'interest-only' loan, you have to get rid of your capital a little bit at a time to pay back the loan. In essence, you will pay back 1/3 of your principal the first year... and then you have to keep making the same Fixed interest + principal payments out of a smaller base of capital.  So for the first few months you can cover the interest easily, but by the end you have to be making phenomenal returns to cover it.  Here is how I would build a model for it (I actually did... and your breakeven is about 1.019% per month. At that outstanding 12.228% annual return you would be earning a whopping $4.) At least as far as the variables are concerned, you need to be considering: Your current capital balance (because month 1 you may have $10,000 but month 2 you have just 9,619 after paying back some principal).  Your rate of return (if you do this in Excel you can play with it some, but you should save the time and just invest somewhere else.) Your actual return that month (rate of return * existing capital balance).  Loan payment = 432 for the parameters you gave earlier.  Income tax = (Actual Return) * (.25). With this kind of loan, you're not actually making enough to preserve the 10,000 capital and you're selling everything you've gained each month.  Commission = ($25 per month) ... assuming that covers your trade fees and broker commissions. I guarantee you that this is not the deal breaker in the model, so don't get excited if you think I'm over-estimating this and you realize that Scottrade or somewhere will let you have trades at $7.95 each.   Monthly ending balance == next month's starting capital balance.  Stack it all up in Excel for 24 months and see for yourself if you like. The key thing you left out is that you're repaying each month out of capital that you'd like to use to invest with. This makes you need much higher returns.  Even if your initial description wasn't clear and this is an interest-only loan, you're still looking at a rate of about 7.6% annually that you need to hit in order to just break even on the costs of holding the loan and transferring your gains into cash. The most tax efficient way to get some cash would be to sell some stocks from the Fidelity account that have the lowest capital gains. The tax will typically be 15% of the capital gains. This will be a one-time cost which should save you money compared to paying 7.5% on the loan year after year. Tax on selling the stock options will probably be higher, since you imply there would be high capital gains, and some of the proceeds might even be taxed as income, not capital gains. How you are taxed will depend on what kind of stock awards they are. The value will be determined by the company that issues it, and appropriate tax forms will be sent to you to include with your taxes. The way the value is determined is an accounting question that is off-topic here, but the value will be stated on your stock award paperwork. If you are awarded the stock directly then that value will be taxed as ordinary income. If you are awarded options, then you can purchase the stock to start the clock on long-term capital gains, but you will not incur any tax liability through the initial purchase.  If the company is sold privately and you have held the stock for over 1 year, then yes, it will be taxed as a long-term capital gain. If you receive/exercise the stock less than 1 year before such an acquisition, then it will be considered a short-term capital gain and will be taxed as ordinary income. The point of a total return index is that it already has accounted for the capital gains + coupon income. If you want to calculate it yourself you'll have to find the on-the-run 10y bond for each distinct period then string them together to calc your total return. Check XLTP if they have anything "Assuming U.S. law, there are ""safe harbor"" provisions for exactly this kind of situation. There are several possibilities, but the most likely one is that if your withholding and estimated tax payments for 2016 totaled at least as much as your tax bill for 2015 there's no penalty. For the full rules, see IRS Publication 17." First, if your stock is trading at $1 and you transfer the 5000 shares in-kind to your TFSA on August 2, 2011, you are deemed to have disbursed that stock in your (assumed) non-registered account. This may have tax consequences depending on the ACB of the original purchase. As for your TFSA overcontribution, you will only have to pay the 1% monthly penalty on the value of the overcontribution, i.e. $5000. You will pay 1%/month for each month the overcontribution exists, regardless of what the value of the overcontributed assets end up being. Thus, you'll pay a $250 penalty for an overcontribution life of 5 months. The stock price could go to $2 or $0, but you'll pay a fixed tax of $250 for the value of the initial overcontribution. See these articles at the CRA website for more information:Tax payable on excess TFSA amount and Examples - Tax payable on excess TFSA amount. "A nondividend distribution is typically a return of capital; in other words, you're getting money back that you've contributed previously (and thus would have been taxed upon in previous years when those funds were first remunerated to you). Nondividend distributions are nontaxable, so they do not represent income from capital gains, but do effect your cost basis when determining the capital gain/loss once that capital gain/loss is realized. As an example, publicly-traded real estate investment trusts (REITs) generally distribute a return of capital back to shareholders throughout the year as a nondividend distribution. This is a return of a portion of the shareholder's original capital investment, not a share of the REITs profits, so it is simply getting a portion of your original investment back, and thus, is not income being received (I like to refer to it as ""new income"" to differentiate). However, the return of capital does change the cost basis of the original investment, so if one were to then sell the shares of the REIT (in this example), the basis of the original investment has to be adjusted by the nondividend distributions received over the course of ownership (in other words, the cost basis will be reduced when the shares are sold). I'm wondering if the OP could give us some additional information about his/her S-Corp. What type of business is it? In the course of its business and trade activity, does it buy and sell securities (stocks, etc.)? Does it sell assets or business property? Does it own interests in other corporations or partnerships (sales of those interests are one form of capital gain). Long-term capital gains are taxed at rates lower than ordinary income, but the IRS has very specific rules as to what constitutes a capital gain (loss). I hate to answer a question with a question, but we need a little more information before we can weigh-in on whether you have actual capital gains or losses in the course of your S-Corporation trade."