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Maximum open orders and positions: broker limits that can break a strategy

Most brokers have limits on how many open positions and pending orders you can have at once. The limits are usually generous, often in the hundreds, so most traders never hit them. But some strategies do.

Grid strategies, EAs that place many pending orders, or traders who scale in with many small positions can bump into these limits. When they do, new orders are rejected, which can leave a strategy half executed. A grid might have orders on one side but not the other. A scaling plan might stop partway.

There are also limits on order size per ticket, total exposure per symbol, and sometimes the number of orders per second. An EA that sends many orders quickly might get rate limited, with some orders rejected or delayed.

The limits are usually in the account specifications or the broker's terms. If not, support can tell you. MT5 also shows some limits in the symbol properties.

If your strategy relies on many orders, check the limits before going live, and make sure the EA handles a rejected order sensibly. It shouldn't keep retrying endlessly, and it should log what happened.

For most manual scalpers, this never matters. For EAs and certain styles, checking once is sensible.

Prop firms often have their own limits on top of the broker's, like a maximum number of open positions or a maximum lot size per trade. These can be much lower than the broker limits. If you run an EA on a prop account, the firm's limits are the ones that matter. Hitting them might also count as a rule breach rather than just a rejected order, so it's important to know them before the EA runs. The firm's FAQ usually lists them, sometimes buried in a section about trading rules.

For MT4 and MT5, the account limits are visible in a few places. Symbol specifications show maximum lot sizes. The account itself might have a limit on total orders, which some brokers display in the account info. If an order is rejected because of a limit, the journal tab usually shows the reason. Logging these rejections in an EA, with the error code, makes it clear whether a missed trade was due to a limit rather than a strategy decision. If an EA hits a limit, the order is usually rejected with an error code, so logging those errors makes the cause obvious quickly.

Grid strategies and EAs with many pending orders are the most likely to hit these limits. When the limit is reached, new orders are rejected, which can break the strategy's logic.

Checking the broker's limits before running such an EA is essential. The EA should also handle the rejection error correctly, so that it does not keep trying to place orders and flooding the server.

The limit on pending orders can surprise grid style EAs or traders who place many orders in advance. Some brokers count pending orders toward the overall limit, others have a separate limit for them. If an EA places twenty pending orders and the broker allows only fifteen in total, the last five get rejected, and the EA might not handle that well. Testing on a demo with the same broker and account type shows what happens. The error codes in the journal make it clear which limit was hit. The broker's support can usually confirm the exact limits too.

How do these limits work across several EAs on the same account? The limit is usually per account, not per EA, so three EAs each opening ten trades could hit a thirty position limit together. If one EA is aware of the limit and the others aren't, the first to open trades gets priority and the others fail. A shared count, or simply knowing the total maximum and setting each EA's own limit to stay well within it, avoids conflicts. It's easy to forget when adding a new EA to an account that's already running others.