How to Calculate the Expected Move
There are two everyday ways to put a number on how far a stock is expected to move around earnings: read it off the option straddle, or compute it from implied volatility. Both land in the same place; here's the arithmetic for each, with worked examples.
Method 1 — the straddle
Find the expiration just after the earnings date. Add the price of the at-the-money call and the at-the-money put — that's the straddle. It's the market's dollar estimate of the swing:
Expected move (%) ≈ straddle price ÷ stock price
On a $100 stock, if the ATM call is $4.20 and the ATM put is $3.60, the straddle is $7.80 — an expected move of about ±7.8%. Some traders multiply the straddle by ~0.85 to isolate the one-standard-deviation move, since the raw straddle slightly overstates it; for a quick read the unadjusted number is fine.
Method 2 — from implied volatility
If you have the implied volatility (IV) of the near-term options, the one-standard-deviation expected move over the option's life is:
Expected move (%) ≈ IV × √(days to expiration ÷ 365)
A stock with 60% IV and 4 days to expiration has an expected move of 0.60 × √(4/365) ≈ 0.60 × 0.105 ≈ 6.3%. The same relationship run backwards lets you infer the IV the market is charging from an observed implied move — the calibration tickerseer uses internally.
Turning the move into strikes
Once you have the expected move, the boundaries are simply the stock price plus and minus that percentage. A $100 stock with a ±7% expected move is priced to land, two times out of three, between roughly $93 and $107. Those edges are where many traders anchor the short strikes of a defined-risk spread — selling premium at or beyond the expected move rather than fighting IV crush with a long option. See the implied move explained for how this reads as a hurdle before a trade.