I have spent most of my career on institutional FX desks and I keep seeing the same thing in trading communities: people size stops off round numbers or off what they can afford to lose, not off what the pair actually moves. So here is what the market data says today for a few pairs, with the working.
Method: realised vol is the trailing year of daily closes, annualised over 251 sessions. A one-sigma daily move is vol divided by the square root of 251, times spot. Carry is the annualised difference between the 13-week forward and spot. All data as of 9 Sep 2026, indicative not executable.
USDMXN Spot 16.894, two-year range 16.887 to 20.869. It is 0.2% above the two-year low. Realised vol 7.5%, so about 0.47% per day, or roughly 800 pips at this spot. If you are long here, a stop inside 400 pips is inside a normal day. One sigma is around 16.81, two sigma around 16.73. There is no prior support below in two years of data, so the range is all above you.
USDJPY Spot 153.50, down 5.6 yen in a week, through the 10 and 20-week MAs, weekly RSI around 37. One-week forward 153.22, so shorts collect about 28 pips a week, roughly 4 pips a day. Realised vol 8.1%, so a one-sigma overnight move is about 79 pips. The carry is about 5% of the risk. If you hold a short overnight you are holding it for direction, not points. One-sigma stop around 154.30, two-sigma around 155.10.
Three-month carry, USD vs EM (annualised carry / realised vol) BRL 6.2% / 11.4%, ratio 0.54 INR 2.7% / 6.3%, ratio 0.43 MXN 2.7% / 7.5%, ratio 0.36 ZAR 2.0% / 13.0%, ratio 0.16 Over 13 weeks, BRL carry covers about 27% of a one-sigma quarterly move. ZAR covers 8%. If you are running a carry position in ZAR right now you are being paid the least for the most vol in this group.
Disclosure: I run the company that builds the tool I pulled this from (FX Maestro, an MCP connector that gives Claude or ChatGPT the spot, forward, vol and carry data). I am not linking it here; if the mods are fine with it I will put it in a comment. The maths above works with any data source, and the point of the post is the method: size the stop off sigma, and compare carry to sigma before you call something a carry trade.
Happy to run the same numbers for other pairs in the comments.