Life Gauge Calculation and Timing Windows in beatmania IIDX

Table of contents
  1. Gauge types
    1. IIDX a-value explained
  2. Timing window
  3. Further reading

Gauge types

For a simple, high-level explanation of each gauge types, please see this page.


  • a = a function of total note count in IIDX – see below
  • all units in %
  • For EASY and NORMAL, you start at 22%, and need 80% in the end of a song to clear. For ASSIST EASY, you start at 22% but need 60% to clear.
  • HARD, EXHARD, DAN, and EX-DAN gauges are “survival” gauges - you start at 100%, and get a stage fail if you drop to 0%.
  • 空P is excessive poor.
A.EASY a a a/2 -1.6 -4.8 -1.6 -
EASY a a a/2 -1.6 -4.8 -1.6 -
NORMAL a a a/2 -2 -6 -2 -
HARD 0.16 0.16 0 -5 -9 -5 Yes
EXHARD 0.16 0.16 0 -10 -18 -10 No
DAN 0.16 0.16 0.04 -1.5 -2.5 -1.5 Yes
EX-DAN 0.16 0.16 0.04 -3.0 -5.0 -3.0 No

† Low Life Adjustment: when the gauge is at or below 30%, the rate of decrease caused by BAD and POORs are halved. For example, when playing on HARD gauge, if you are at 28% life and get a POOR, you lose 4.5% instead of 9%.

IIDX a-value explained

Graph explaining what the a-value means in IIDX

Timing window

timing diagram

JUDGE Window (ms) Resets combo
PGREAT ±16.67 No
GREAT ±33.33 No
GOOD ±116.67 No
BAD ±250 Yes
POOR at -250 Yes
空POOR ? No

All units in milliseconds. Positive means before the note, negative is after the note.

Pressing a button within the BAD window counts as judgement for that note, and “erases” the note from view.

Regular POOR happens if you don’t press a button within the late BAD window. This resets the combo.

FAST 空POOR happens if you press a button slightly before the FAST BAD window. This does not erase the note.

SLOW 空POOR happens if you press a button again slightly after pressing it to count toward the judgment of a note (the first press will be a BAD or greater, and the second press will be a POOR). If the button press happens to be within the next note’s BAD window, that it will count towards that instead.

For Charge Notes (and Back Spin Scratch):

  • if you get BAD or POOR on the start of a CN, there is no judgement for at the end of a CN (no impact on life gauge, does not in crease any numbers in JUDGE window)
  • the “release” judgement window at the end of a CN is significantly wider, but exact numbers are not known

It is possible for some charts to have more restrictive timing windows; the most notable one is GAMBOL.

It is a myth that timing windows are larger in DP.

It is a myth that the timing windows are asymmetric; the timing windows themselves are the same duration before and after the precise timing. It is not larger on one side.

That being said, there are various factors that may make it seem like the entire timing window slightly shifted towards the “fast” side (frame quantization, input capture window, etc) - but it is at most 1 frame difference.

Further reading

IIDX LR2 beatoraja differences

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