By the time a central bank announces a decision, the market has spent weeks pricing the probability of it. Where the outcome matches expectation, the number itself changes very little. What moves price is the difference between what was expected around the decision and what is actually said.
The parts that carry information
The statement’s wording
Changes of a few words in the forward-looking paragraph are read closely, because they are chosen closely.
The vote split
A unanimous decision and a narrow one imply very different odds for the next meeting.
Updated projections
Where a bank publishes forecasts, revisions to growth and inflation paths often move price more than the rate itself.
The press conference
Frequently the largest movement of the session, and it happens well after the headline has been reported.
Practical consequences for execution
Spreads widen sharply in the seconds around the release and again when the press conference begins. Liquidity thins in the same window, so slippage is at its largest exactly when the movement is fastest. A position that is comfortable at normal spreads can be uncomfortable at release spreads without the market having moved against you at all.