A plain-English guide to FOMC-eve gamma compression.

Tuesday's analysis piece is the live example. Empire State and NAHB both printed dovish, but the tape's response was proportionate rather than violent, with DXY moving 10 pips and the 10-year moving 1.7bp on prints that would normally deliver 20+ pips and 3-5bp of intraday move. This reference piece is the framework for reading FOMC-eve gamma compression, which explains why the tape reacted less than the surprise implied and how the dampened response feeds the Wednesday decision setup.

What FOMC-eve gamma compression is

Gamma compression is the market's option-book expression of "the next major event is close and it dominates all other pricing until it lands." On the day before an FOMC decision, dealers hedging their options books are running short gamma positions in DXY and short gamma positions in rates, because their overnight vol books are marking to the FOMC-crossing tenor's implied vol rather than to realised. Short-gamma hedging pushes dealers to sell into strength and buy into weakness on any intraday move, which mechanically dampens the tape's response to unrelated intraday catalysts.

In practice, an economic release on the day before an FOMC decision produces a tape reaction that is roughly 30 to 50 percent smaller than the same release would produce on a non-FOMC-eve day. The size of the compression is directly proportional to the option book's positioning going into the event: bigger short-gamma positioning means more compression.

The three signatures of FOMC-eve gamma compression

Three specific tape signatures identify the compression regime:

Signature 1: catalyst reactions dampened by 30-50 percent. Empire State prints 7.4 points below consensus; on a normal Tuesday the DXY reaction would be roughly 20-30 pips; on FOMC-eve Tuesday the reaction is 8-12 pips. This is the specific footprint Tuesday September 15, 2026 delivered on Empire State: the print was 7.4 points below consensus, and the initial DXY reaction was 12 pips (about 50 percent of the "normal" size). NAHB's second impulse two hours later was 8 pips, again about half the size of the equivalent non-eve reaction.

Signature 2: implied vol premium widening into the close. The overnight FX vol on the FOMC-crossing tenor trades progressively wider through the Tuesday afternoon session. A 25 percent premium to trailing-five-session realised vol is normal for FOMC-eve; a 35 percent premium is elevated and signals the market is nervous about the tail; below 15 percent is committed. Tuesday closed at a 28 percent premium in DXY, consistent with a "priced for proportional response, some residual tail risk" reading.

Signature 3: two-way ranges collapse. Realised range on FOMC-eve is typically 40 to 55 percent of the trailing 20-session average. Tuesday DXY's range was 32 pips versus a trailing average of 48 pips, roughly 67 percent, which is elevated for FOMC-eve. That is the specific signal that the two data prints (Empire State at 8:30 and NAHB at 10:00) added some genuine intraday range that would not have appeared on a data-free FOMC-eve.

How compression feeds the Wednesday reaction

Gamma compression on FOMC-eve builds an under-priced dispersion into the Wednesday decision. When the FOMC delivers a hawkish surprise, dealers with short gamma have to buy dollar into a rising DXY (mechanical hedging), which amplifies the initial move by 20 to 40 percent versus a "no compression, unhedged" baseline. Conversely, when the FOMC delivers a dovish surprise, dealers have to sell dollar into a falling DXY, again amplifying the initial move by 20 to 40 percent.

The framework's practical implication is that the FOMC reaction on Wednesday will be more violent than the surprise magnitude alone would predict, because the compressed Tuesday tape has pushed the option book into a short-gamma posture. A 10bp surprise on the SEP median (either direction) produces roughly 80 to 120 pips of DXY move; a 20bp surprise produces 150 to 250 pips.

The role of the Chair's first press conference on gamma

The specific setup on September 16, 2026 has a wrinkle the framework does not usually see: it is Kevin Warsh's first FOMC as Chair with a full SEP and press conference. Traders have no calibration for his press conference cadence, his verbal cues, or his willingness to deviate from the statement's language during Q&A. That uncertainty is showing up in the vol book as a wider premium in the press conference tenor (14:30 to 15:30 ET) than in the statement tenor (14:00 to 14:30 ET). The market is pricing Warsh's press conference as more dangerous than the statement itself.

In practice this means the Wednesday tape may deliver two separate impulses. First move on the 2:00 PM ET statement plus SEP release; second move on Warsh's 2:30 PM ET press conference. The two impulses can amplify each other (both hawkish or both dovish) or partially cancel (statement hawkish, press conference softer, or vice versa). The framework's read on which outcome is more likely: Warsh's press conference typically hews closer to the statement's language than his predecessors did, so the two impulses are more likely to compound than to cancel.

Related reading

• Tuesday's analysis piece: the live example this framework describes.
• FOMC day tape: the two-hour repricing mechanic on decision day.
• Keynote-eve gamma compression: the analog framework for a Chair keynote (Jackson Hole) rather than an FOMC decision.
• SEP and dot plot: the specific projection the September meeting builds.
• Forward guidance: the language hooks in the statement and the press conference that carry the signal.