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Partial fills on ECN accounts when the book is thin

Partial fills catch newer ECN users off guard. A ten-lot order gets four lots at one price, three at the next, and the rest wherever the book allows. On a scalp with a four-pip target, that spread of fills changes the entire math.

The issue is worst on crosses and exotics during off-peak hours, when the depth at the best price might be a single lot or two. The platform shows one number, yet the volume-weighted average entry sits well away from it.

Some platforms offer fill policies like fill-or-kill, immediate-or-cancel, and return. Each behaves differently. Fill-or-kill rejects the whole order if full size is not available, which protects entry price at the cost of missed trades. Immediate-or-cancel takes what exists and drops the rest.

For scalpers, a partial fill also creates awkward position sizes, with stops and targets that no longer match the intended risk.

A practical habit is scaling order size to the visible depth instead of the account balance.

How is size handled on thinner pairs, and has a policy like fill-or-kill ever saved a trade?

Happened to me on EUR/NZD in the late New York session. Sent a 3 lot market order, got 1 lot at the quoted price, 1 at 0.4 pips worse, and the last 1 at 1.1 pips worse. Average entry 0.5 pips off the quote. On a 5 pip target, that's 10 percent gone before the trade started. And the stop was placed relative to the first fill, so the risk on the full position was slightly bigger than planned. Now I don't trade more than 1 lot on crosses outside the main sessions.

Partial fills hurt me first on gold at an ECN broker during the Asian session. I sent a 2 lot market order with a 3 dollar target and got 0.8 lots at the quote, 0.7 at 35 cents worse and the last 0.5 at 90 cents worse. The average entry was around 45 cents off, which is 15 percent of the target gone at once, and the platform showed three separate positions to manage.

What helped was reading the order book depth where my platform showed it, and sending no more than about half of what was visible at the touch. When I needed more size, I split it into two orders a few seconds apart instead of one large one.

I also tried the immediate or cancel option on my terminal, and on thin pairs it saved me several awkward half-filled trades in a month. I accept a missed trade much more easily now than a position at a size I did not plan, because the stop distance was calculated for the full order.