Maximum spread filters and their blind spot

[Amanhasnoname]

A rule that says 'no trade if the spread exceeds X pips' is among the most useful filters in scalping. It protects against rollover, news, and illiquid moments.

The blind spot is that the spread at the moment of the click is not always the spread at the moment of the fill. During fast moves, the spread can widen between the decision and the execution.

Another gap is the time of day. A fixed threshold, say 1.2 pips, might be too tight at the Asian open for some pairs, blocking all trading, and too loose at the London open, allowing poor fills.

A time-aware threshold is better: a different limit for each session, based on the typical spread at that time. For example, 1.5 times the median for the hour.

For automated systems, the check should happen right before sending, with the latest quote, and the order should include a deviation limit to catch changes.

How is the spread limit set, and does it differ by session?