What's wrong with this margin calculation?
As the referenced document says, there are 3 formulas, and you need to use the formula which results the greatest margin requirement. In your case, you need to use the 10% formula:
Another way to look at this is if we separate the owner's account from the business's account.  At the start of the year, the owner puts $9 into the business account to get the business started. At the end of the first day, the business account has $10, and at the end of the second day, the business account has $11.  The owner doesn't need to add any more of his own money into the business account. At the end of the 365th day, the business will have $374, which is $365 profit + $9 investment.  Assuming the business has no other expenses, the business will calculate profit for the year like this: The author is making a strange point. The two numbers he is talking about are two different quantities. The business owner's return on investment is $365 / $9 = 4056%.  But the business's profit margin is $365 / $3650 = 10%.  Both are useful numbers when running the business. I disagree with the author's insinuation that a business is doing something tricky when calculating profit margin. Remember that, in addition to the business owner's monetary investment, he worked every day for a year to earn that $365. Wrong. If an industry needs 3 widget makers, and there are only 2 widget makers on Earth, their salary is going to be dramatically higher  (and thus cut into margins) than a world where 3 are needed but 30 exist.   To claim that supply and demand doesn't exist in the labor market or isn't a primary driver of wages is so fallacious that it's nothing short of retarded. "Ah .. I don't know Chicago very well, but several classmates ended up there and report that real estate + tax are expensive. Here in Philadelphia, several marginal neighborhoods are in the middle of a real estate boom (some say bubble). People are demanding new construction, but don't care where it is. 600k for a row home is pretty common in Kensington. Same old gentrification story .. first the artists moved in for cheap rents, then coffee shops and then the developers. For those not aware, those parts of Kensington was ground zero for the 1980's crack/crime epidemic .. only the most marginal of blue collar workers couldn't afford to leave.   Sounds like Gary, Ind got themselves on the wrong side of that line. Maybe in a couple decades it will get ""rediscovered"". Kinda sad, but we do have a history of letting places fail (eg. Wild West ghost towns)." "From the IRS perspective, there's no difference between ""your taxes"" and ""your sole proprietorship's taxes"", they're all just ""your taxes"". While I could see it being very useful and wise to track your business's activities separately, and use separate bank accounts and the like, this is just a convenience to help you in your personal accounting, and not something that needs to relate directly to how tax forms are completed or taxes are paid. When calculating your taxes, if you want to figure out how much ""you"" owe vs. how much ""your business"" owes, you'll have to do so yourself. One approach might be just to take the amount that your Schedule C puts as income on your return and multiply by your marginal tax rate. Another approach might be to have your tax software run the calculations as though you had no business income, and see what just ""your personal"" taxes would have been without the business. If you think of the business income as being ""first"" and should use up the lower brackets rather than your personal income, maybe do it the other way around and have your software run the calculations as though you had only the business income and no other personal/investment income, and see what the amount of taxes would be then. Once you've figured out a good allocation, the actual mechanics of paying some ""personal tax amount"" from your personal bank account and some ""business tax amount"" from your business bank account are up to you. I'd probably just transfer the money from my business account to my personal account and pay all the taxes from the personal account. Writing two separate checks, one from each account, that total to the correct amount, I'm sure would work just fine as well. You can probably make separate payments from each account electronically through Direct Pay or EFTPS as well. As long as all taxes are paid by the deadline, I don't think the IRS is too picky about the details of how many payments are made." "Meh. Nice Feature article, but some things pop out.  1.  ""The guy doesn't understand his strategy""? uhhh   1.  10 million is small and I don't know how well that would scale up. 1.  Plus this guy works full time at a university. How many investor would give money to a guy not dedicated full time. Maybe he can raise small amounts from a large audience, but I don't think people would give him anything substantial. Perhaps a trial basis, but I think there's a ceiling 1. Is it really ""AI""? people forwarded me some of his notes and it looks more just like graph theory. (could be wrong on this)" To calculate any daily return, all one need do is divide the final value by the initial value, subtract 1, and multiply by 100%: This can be applied to either the futures alone, the investments used as margin collateral alone, or all together. Margin collateral as a factor of a derivative's return Collateral can take many forms. Many suggest that cost and revenue for a derivative trade should also take into account margin requirements.  This can become problematic. If a futures position moved against the trader, yet the margin was secured with equities at the maximum, and the equities moved with the trader, the futures trade could be interpreted as less of a loss because the collateral, which is probably totally disassociated with the futures position, increased in value. Then again, if a futures position moved with the trader, yet the margin collateral moved against the trader then taken together, the futures trade would look less profitable. Furthermore, most likely the result of a futures position and its collateral would never produce the same result, so extrapolation would become ever more difficult. For ease of analysis, a position's cost and revenue should be segmented from another unless if those positions are meant to hedge each other.  Margin is not a cost, but it is a liability, so margin will affect the balance sheet of a futures trade but not its income statement, again unless if the collateral is also used to hedge such futures position. The author is using the simple Dietz method, (alternatively the modified Dietz), with the assumption that the net cash-flow occurs halfway through the time period.  Let's say the time period is one year for illustration, so the cash-flow would be at the end of the second quarter. The money-weighted method gives a more accurate return, but has to be solved by trial-and-error or using a computer.  The money-weighted return is 11.2718 % and the simple or modified Dietz return is 11.2676 %.  When the sums are done backwards to check, the Dietz is half a dollar out with a final value of $11,999.50 while the money-weighted return recalculates exactly $12,000. It is worth pointing out that the return changes if the cash-flow is not in the middle of the time period.  A case with the cash-flow at the end of Q3 is added to illustrate. As your question is written now, it looks like you have a typo.  Your stated APR is 5.542% = 0.05542, not 0.005542 as you've written.  I ran the numbers that you gave (accounting for the typo) through the formula at Wikipedia and got $849.2528 / month, which will round to $849.25 for most payments.  That doesn't match the number that you computed or the number on your TIL. (Maybe you also miskeyed the result of your calculation?) I agree that it's unlikely that this is just a calculation error by the mortgage company, although I wouldn't completely rule it out.  Are you paying anything else like a property tax escrow?  I didn't pull a blank TIL form to see what might go into the monthly payment line that you showed, but in many cases you do pay more than just principle and interest each month. (Not sure if that gets reflected at that point on the form though.)