Break of Structure (BOS): when price takes out the last swing
A break of structure happens when price closes beyond the last confirmed swing high in an uptrend, or the last confirmed swing low in a downtrend. It says the trend just made a new leg, and it turns into a clean rule once you pin down what counts as a swing.
What it measures
Everything depends on the swing definition, which discretionary traders usually skip. A swing high is a bar whose high is above the highs of the L bars before it and the R bars after it; a swing low is the mirror image. The swing only exists once those R bars have printed, so it is always confirmed late.
The rule: in an up structure, a bullish break of structure is the first close above the most recent confirmed swing high, written as close > last swing high. In a down structure it is the first close below the last confirmed swing low. A close beyond a swing against the current structure is a change of character, the first hint that the structure may be flipping.
Close or wick? I'd use the close. A wick through the level that closes back inside is a sweep, a different event.
How it behaves in real markets
In steady trends on NQ, breaks come in a rhythm: push, pullback, new swing, break. In ranges the rule fails again and again, because each poke above the last swing high gets sold back into the range. Those failed breaks are the main cost.
The R bars are a real limitation. A large R gives cleaner swings that are old by the time they are known; a small R turns every wiggle into a swing.
Common ways to use it (concepts)
Enter on the break
Go with the trend on the first close beyond the last swing, stop beyond the swing before it. Simple, and it gets chopped up in ranges.
Wait for the pullback to the broken level
After a break, wait for price to come back to the old swing level and hold. Fewer trades, better location, and some breaks never come back.
Trade the break that doesn't hold
A close beyond the swing that falls back inside within a few bars is a failed break. Some traders fade it.
Pairing it with other indicator families
Structure gives direction and timing but nothing about size. ATR helps decide whether a break is meaningful or a tick through the level, and sizes the stop.
For the range problem, add a regime check such as ADX, or require a Supertrend line to agree. A second structure rule with a different swing size isn't confirmation. It is the same idea twice.
In AlphaPrime
AlphaPrime has a built-in market structure family. It confirms swings with a left and a right bar count and gives the strategy generator conditions for a break of structure, a change of character, liquidity sweeps, retests, failed breaks, equal highs and lows, and where price sits between the last swings.
Put the continuation rule and the failed-break rule in the same run. They are opposite bets on the same event, and the out-of-sample stretch shows which one your market rewards. The free seven-day trial is enough to start.
FAQ
What is the difference between a break of structure and a change of character?
A break of structure goes with the current structure, a new high in an uptrend. A change of character goes against it, the first close below the last swing low.
How many bars should confirm a swing?
There's no correct count. Fewer bars give fresher levels and more noise; let the generator test a range.
Is break of structure just a breakout?
Close to it. A plain breakout uses the highest high of a fixed window, like a Donchian Channel; a break of structure uses the last confirmed swing.