Last, Fair or Index? Picking the trigger price for an ADA short stop on MEXC, with the 0-fee math (intermediate TP/SL)

On MEXC you choose which of the three your take-profit and stop-loss watch, and that one setting decides how your stops react to wicks.

The three trigger prices on MEXC

• Last Price is the latest trade on MEXC's own order book. It reacts fastest, including to brief local spikes.
• Fair Price is MEXC's smoothed reference price, built to be less jumpy than the last trade.
• Index Price tracks the underlying spot market rather than one order book, so a local wick moves it less.

MEXC also offers Price Protection, which it describes as helping prevent abnormal stop-loss and take-profit triggers in extreme volatility. Worth turning on if you use Last Price.

The ADA market at 9:54 AM ET, MEXC public data

ADA_USDT last 0.1901, fair 0.1901, index 0.1903, down 1.5% on the day, with a 24 hour range of 0.1894 to 0.1949. One contract is 1 ADA. The pair showed a 0% maker and 0% taker rate in the contract data. Funding was 0.0071% per 8 hours, maintenance margin 0.23%.

The screenshot is the live MEXC ADAUSDT perp page at 9:57 AM ET: 0.1896, down 1.76%, index 0.1898, fair price 0.1897, funding +0.0069% with 01:02:05 left, 24h high 0.1949 and low 0.1894, the 0 Fees tag, a 15m chart with the Last Price toggle, and the order book.

Worked example (example, not a recommendation): account 1,200 USDT, risk 1% (12 USDT), short at 0.1901, stop 0.1955 above the 24h high, target at 2R.

1. Stop distance: 0.1955 - 0.1901 = 0.0054 per ADA, about 2.84%.
2. Fees: 0% in and 0% out on this pair at fetch time, so nothing to add.
3. Size: 12 / 0.0054 = 2,222 ADA, which is 2,222 contracts and about 422.40 USDT of value.
4. Target: 0.1901 - 2 x 0.0054 = 0.1793. Gain about 24.00 USDT, a clean 2.00R, since fees are zero.

On a venue charging 0.06% taker, the same trade would lose a slice of R to fees. Here the only drag is funding and slippage. At 0.0071%, a short receives about 0.03 USDT per 8 hours on this size while the rate stays positive.

Which trigger for this trade?

The stop sits just above the 24h high, exactly where a quick wick would poke through. Fair or Index makes that kind of stray trigger less likely. The trade-off is that on a real breakout, an Index-based stop can fire a moment after Last has already moved, so the fill may be a little worse. The take-profit is less sensitive to this and Last is fine there.

The leverage trap

ADA_USDT allows up to 300x. At 50x, initial margin is 2% of value, and after 0.23% maintenance there is about 1.77% of room, less than the 2.84% stop. Liquidation would come first. At 20x the room is about 4.77%. At 10x the margin is about 42.24 USDT.

Common mistakes

• Why did my stop trigger when the chart never got there? Your chart may show one price type and the stop may watch another.
• Why did my stop not trigger on a wick? It was on Fair or Index, which smoothed the spike out.
• Why does zero fees not mean zero cost? Funding and slippage still apply.
• Does this carry over to BTC, ETH, XRP or DOGE? The logic does, the contract size may not.

Short FAQ

Should the take-profit use the same type as the stop? Not necessarily. Last on the TP and Fair or Index on the SL is a common split.

Is a trailing stop a separate thing? Yes, MEXC offers it as its own order type.

Will fees stay at 0%? Rates can change by pair, so check the contract details before each trade.

Next time you open the ADA perp, look at last, fair and index side by side for a minute. The gap between them is the noise your stop setting either listens to or ignores.