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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


  • a = a function of total note count in IIDX – see below
  • all units in %
  • For EASY, NORMAL, and HARD, you start at 2%, and need 80% in the end of a song to clear. For ASSIST EASY, you only need 60% instead.
  • 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

JUDGE Window (ms)
PGREAT ±16.67
GREAT ±33.33
GOOD ±116.67
BAD ±250

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

In IIDX, it is possible for some charts to have more restrictive timing windows; the most notable one is GAMBOL.

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