how to check maximum lot size for a broker account type in code?

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Jackery
92
Jackery  
I am writing an EA and need to be able to check the maximum lot size for a broker's account type in code, so I can place an alert or something if the size is ecxeeded. How can this be done?
William Roeder
20228
William Roeder  
If you are worried about maximum lot size, you are not controlling your risk. Never risk more than a small percentage of your account, certainly less than 2% per trade, 6% total. In code (MT4): Risk depends on your initial stop loss, lot size, and the value of the pair. It does not depend on margin and leverage.
  1. You place the stop where it needs to be - where the reason for the trade is no longer valid. E.g. trading a support bounce the stop goes below the support.
  2. AccountBalance * percent/100 = RISK = OrderLots * (|OrderOpenPrice - OrderStopLoss| * DeltaPerLot + CommissionPerLot) (Note OOP-OSL includes the spread, and DeltaPerLot is usually around $10/pip but it takes account of the exchange rates of the pair vs. your account currency.)
  3. Do NOT use TickValue by itself - DeltaPerLot and verify that MODE_TICKVALUE is returning a value in your deposit currency, as promised by the documentation, or whether it is returning a value in the instrument's base currency.
              MODE_TICKVALUE is not reliable on non-fx instruments with many brokers - MQL4 programming forum 2017.10.10
              Is there an universal solution for Tick value? - Currency Pairs - General - MQL5 programming forum 2018.02.11
              Lot value calculation off by a factor of 100 - MQL5 programming forum 2019.07.19
  4. You must normalize lots properly and check against min and max.
  5. You must also check FreeMargin to avoid stop out

Most pairs are worth about $10 per PIP. A $5 risk with a (very small) 5 PIP SL is $5/$10/5 or 0.1 Lots maximum.

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