Theta Is Rent, and I Was Always the Tenant

A Sunday, a kitchen table, a year of fills exported to a spreadsheet. I had wanted to check something else entirely. I added a column for days held. Another for theta at entry. Then I multiplied the two and summed the result.

Then I sat looking at that total for longer than I want to admit.

The arithmetic I had been declining to do

One contract. A thirty day call bought at $1.60 with theta of $0.04. Stock stands still. Implied volatility holds. It still loses about four cents a share a day, which is 0.04 x 100 = 4 dollars a day for holding it.

Four dollars a day. Hold it ten days waiting for a setup to develop and 10 x 4 = 40. That is a quarter of the $160 premium. The underlying sat exactly where you left it.

Decay does not run at a steady rate. Theta on a near the money option grows as expiration approaches. The final week costs more per day than the first week did, which means the position I thought I was holding patiently was in fact a position charging me a rising rent for every day I extended the lease.

Now multiply by habit. If you keep three long premium positions open most of the time with a combined theta of about twelve dollars a day, then across roughly 250 trading days that is 12 x 250 = 3,000. Three thousand dollars of rent, paid whether or not anything happened, and the only days you earn it back are the days the underlying moves far enough to overcome it.

My journal said exactly what you would expect. Winners came from a small number of decisive moves. Losses came in two populations: the trades where I was wrong about direction, which is fair enough and which I had budgeted for, and the much larger group where I turned out to be right eventually and had spent the whole interval paying for the privilege of waiting.

What I did not conclude

Everybody who does this arithmetic for the first time arrives at the same response. Flip sides. Become the landlord and collect the rent.

Be careful here. The premium a seller collects is payment for accepting the risk of a large move. The calendar hands sellers no edge. A single gap through a short strike undoes a great many quiet Fridays. The distribution of outcomes changes shape, and shape is all it changes. You are choosing which risk you carry, and the new one is lumpier and arrives less often, which is what makes it so easy to mistake for an absence of risk for a year or two at a time.

So the changes I made were smaller and more specific than switching teams.

I stopped using long premium to express a vague view. If I cannot name roughly when the move should happen, I take the position in shares. Or I take nothing.

Where I want defined upside over a known window, I sell a further strike against the one I own, which turns the position into a spread, caps the payoff and cuts the daily bill. The arithmetic is in vertical spreads explained.

On shares I already own and would be content to sell higher, writing a call is the one case where I am straightforwardly the landlord, and the cap on that upside is the real cost. It is not small. Covered calls works through both sides. Strike selection becomes an arithmetic question once the static and if called returns sit next to each other.

The two numbers I write down now

Two numbers go down before any long option position opens: the total theta I will pay if I hold all the way to my intended exit date, and the size of the move in the underlying that would be needed to cover it.

If the move required to break even on carry alone is larger than what I honestly expect over that window, the trade is bad at any premium, and the size of the premium is irrelevant to that conclusion. The check takes under a minute with the options Greeks calculator. Each Greek is worked through with numbers in option Greeks explained.

One thing I am less sure of than I sound. Theta at entry is a snapshot, and it changes as the stock moves and as volatility moves, so summing entry theta across a year is an approximation and probably an understatement for anything I held near the money into the final week. I did the sum the crude way on purpose. A crude number beat a precise one I had been avoiding for a year.

The framing that stuck is the rent one. Something is deducted every day a long option sits in the account, quietly, the way a standing order leaves a current account on the same date each month until you stop noticing it is there.