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Century egg
You gain more CpS the longer you've played in the current session.
"Actually not centuries-old. This one isn't a day over 86!"

Century egg is a "rare egg" upgrade available during the Easter Season.

The Century Egg increases your CpS by a varying amount - depending on how long you have played without resetting. Like other eggs, this multiplier is "global", and is applied after the other multipliers (but it does stack additively with the other eggs).

The longer the session, the higher the multiplier, but with diminishing returns. It takes about 100 days for Century Egg to reach its maximum output of +10% (which allows a total of +22% gain from eggs). The formula is:

where , and "days" is the current session's length.

Note: "days" can be fractional, up to 10 seconds of precision.

Note: This increase is added to the Easter global multiplier.

Note: The bonus is not locked in when you buy the upgrade.  It will continually adjust to the appropriate value based on the length of the current session.

So this gives us the table:

Session started Global CPS
0 hours +0%
24 hours +0.29701%
48 hours +0.58808%
72 hours +0.87327%
96 hours +1.15264%
120 hours +1.42625%
144 hours +1.69416%
168 hours +1.95643%
192 hours +2.21312%
216 hours +2.46429%
240 hours +2.71%
360 hours +3.85875%
480 hours +4.88%
720 hours +6.57%
960 hours +7.84%
1200 hours +8.75%
1440 hours +9.36%
1680 hours +9.73%
1920 hours +9.92%
2160 hours +9.99%
2400+ hours +10%