Friday, January 3, 2014

predicted future px USUALLY exceeds current px - again

This is a pretty important concept ...

Extreme example - Suppose home price is believed to be unpredictable or unstable for the next 3 months[1], and short term rental is impossible, and there are many equivalent houses on sale. You just bought one of these equivalent houses but need it in 3 months and you would have all the cash by then. Do you prefer to "settle" (i.e. pay cash and get key) now (A) or (B) in 3 months? You prefer B because A means you must start paying mortgage interest 3-month earlier.

Now suppose seller exploits your preference for B, and asks $1 more to do a fwd deal (B) instead of a spot deal (A), you would be wise to still prefer B because interest amount is likely to be thousands.

So $1 is too cheap. But what's a fair price for the fwd deal? I think it's exactly the spot price plus the mtg interest amount. For most securities, fwd price [2] is Higher than spot. (A few assets are exceptions and therefore important[3].) First suppose fwd price == spot price as of today, and ignore the positive/negative signs below --

* if interest_1 < rent_3, then seller gains. Some competing seller would sacrifice a bit of gain to sell at a lower fwd price. Fwd price is then driven down below spot price. This is the high-coupon case.
* if interest_1 > rent_3, then seller loses. She would simply reject the proposed trade. She would have to charge a Higher fwd price to compensate for her loss. This is the usual case, where rent_3 is $0 and there's no repo or rent market for this asset.

I feel the fair theoretical fwd price is not affected by implied volatility, or by any kind of trend. A trend can continue or reverse. I feel the calculation of fwd price is based on assumption of constant asset price or random movement for the next x months.

[1] I think in most cases of fair pricing we assume the asset's price has no up/down trend.
[2] If the spot contract doesn't have a pair of start/end dates, i.e. a straightforward "cash-on-delivery" instrument, then I think in many cases "fwd price" means " delayed settlement".

[3] Their fwd price is Lower --
- High-coupon bonds such as treasury
- High-dividend stocks
- many currency pairs

Why the premium vs discount? There's arbitrage mathematics at play. For most products, a fwd seller could 1) borrow cash to 2) buy the underlier today, 3) lend it out for the fwd term (say 90 days), and 4) deliver it on the fwd start date as promised. All deals are executed simultaneously today, so all prices fixed together, and a profit if any is locked in.


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