Fill (Execution)
An order actually executing — partially or fully — and the price reality of it.
What it means
A fill is the moment intent becomes position. Market orders fill immediately at whatever the book offers — including walking through levels when size exceeds the top. Limit orders fill only if price comes to them, which means the worst fills come exactly when you were most right to be urgent.
Partial fills are routine: 1,000 shares wanted, 300 filled, the rest chasing. Automated systems must decide what a partial position means for exits and sizing — pretending fills are always complete is one of the quiet lies backtests tell.
Why traders care
- Fill mechanics — not signals — set the floor on achievable performance.
- Partial-fill handling separates production-grade systems from demos.
Educational content, not investment advice. Engine details describe how TraderWe computes this value; other platforms may define it differently.