Easter season
Easter is a seasonal event in Cookie Clicker. The big cookie will have a nest under it during this time (However, the nest does not appear if the "Particles" setting is off). It was added on May 18, 2014, with the 1.0464 update. Since the 1.0466 update, Easter starts automatically and lasts from 7 days before Easter (Palm Sunday) to Easter itself (Resurrection Sunday).
2024 event period: March 24thMarch 31st. (Note that if Easter season overlaps with Business Day season, the latter takes precedence, temporarily halting Easter season.)
After purchasing the heavenly upgrade Season Switcher, Easter can also be activated for 24 hours by purchasing Bunny biscuit. The upgrade is repeatable, but it gets more expensive each time it is bought, similar to buildings.
Upgrades
There are 20 Upgrades that are from the Easter Season. All upgrades are egg/larvae based in theme and can be unlocked randomly when clicking a Golden Cookie, Wrath Cookie, or popping a wrinkler. The price of purchasing each egg goes up based on the number of eggs purchased so far (E in the chart below).
Icon  Name  Unlock condition  Base price  Description  ID 

Chicken egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "The egg. The egg came first. Get over it." 
210  
Duck egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "Then he waddled away." 
211  
Turkey egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "These hatch into strange, handshaped creatures." 
212  
Quail egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "These eggs are positively tiny. I mean look at them. How does this happen? Whose idea was that?" 
213  
Robin egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "Holy azurehued shelled embryos!" 
214  
Ostrich egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "One of the largest eggs in the world. More like ostrouch, am I right? Guys?" 
215  
Cassowary egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "The cassowary is taller than you, possesses murderous claws and can easily outrun you. You'd do well to be cassowary of them." 
216  
Salmon roe  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "Do the impossible, see the invisible. Roe roe, fight the power?" 
217  
Frogspawn  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "I was going to make a pun about how these "toadally look like eyeballs", but froget it." 
218  
Shark egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "HELLO IS THIS FOOD? LET ME TELL YOU ABOUT FOOD. WHY DO I KEEP EATING MY FRIENDS" 
219  
Turtle egg  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "Turtles, right? Hatch from shells. Grow into shells. What's up with that? Now for my skit about airplane food." 
220  
Ant larva  "Common" egg (see Probabilities) 
999 x 2^{E}  Cookie production multiplier +1%. Cost scales with how many eggs you own. "These are a delicacy in some countries, I swear. You will let these invade your digestive tract, and you will derive great pleasure from it. And all will be well" 
221  
Golden goose egg  "Rare" egg (see Probabilities) 
999 x 3^{E}  Golden cookies appear 5% more often. Cost scales with how many eggs you own. "The sole vestige of a tragic tale involving misguided investments." 
222  
Faberge egg  "Rare" egg (see Probabilities) 
999 x 3^{E}  All buildings and upgrades are 1% cheaper. ^{[note 1]} Cost scales with how many eggs you own. "This outrageous egg is definitely fab." 
223  
Wrinklerspawn  "Rare" egg (see Probabilities) 
999 x 3^{E}  Wrinklers explode into 5% more cookies. Cost scales with how many eggs you own. "Look at this little guy! It's going to be a big boy someday! Yes it is!" 
224  
Cookie egg  "Rare" egg (see Probabilities) 
999 x 3^{E}  Clicking is 10% more powerful. Cost scales with how many eggs you own. "The shell appears to be chipped. I wonder what's inside this one!" 
225  
Omelette  "Rare" egg (see Probabilities) 
999 x 3^{E}  Other eggs appear 10% more frequently. Cost scales with how many eggs you own. "Fromage not included." 
226  
Chocolate egg  "Rare" egg (see Probabilities) 
999 x 3^{E}  Contains a lot of cookies^{[note 2]}. Cost scales with how many eggs you own. "Laid by the elusive cocoa bird. There's a surprise inside!" 
227  
Century egg  "Rare" egg (see Probabilities) 
999 x 3^{E}  You continually gain more CpS the longer you've played^{[note 3]} in the current session. Cost scales with how many eggs you own. "Actually not centuriesold. This one isn't a day over 86!" 
228  
"egg"^{[note 4]}  "Rare" egg (see Probabilities) 
999 x 3^{E}  +9 CpS "hey, it's "egg"" 
229 
Unlocking Eggs
Eggs are unlocked randomly during the Easter season by either popping wrinklers or clicking Golden/Wrath Cookies. The base fail rate to unlock an egg from a Golden/Wrath Cookie is 90% (0.9), while the base fail rate for a wrinkler is 98% (0.98). There are many modifiers that can reduce the fail rate.
Modifier  Factor 

Green yeast digestives  1/1.03=0.970874 
Dragon teddy bear  1/1.03=0.970874 
Santa's Bottomless Bag  1/1.1=0.909091 
Hide & seek champion  0.7 
Omelette  0.9 
Starspawn  0.9 
Selebrak, Spirit of Festivities  0.9/0.95/0.97 (Diamond/Ruby/Jade) 
Mind Over Matter, Reality Bending, both  1/(1.25, 1.025, 1.275) = 0.8, 0.9756, 0.7843 
Cosmic Beginner's Luck  0.2 
Garden plants (mature, dirt)  1/(1+0.01G+0.01S+0.03K) G = # of Green Rot S = # of Shimmerlily K = # of Keenmoss 
For example, if you click a Golden cookie and you have Omelette, Starspawn, Santa's Bottomless Bag and Mind Over Matter, the fail rate is
You can also easily scum when farming eggs drops (and other rare wrinkler's drops). If you pop a wrinkler and reload the page without saving, the wrinkler will come back. Therefore, you can save the game, pop your wrinklers, and if they drop nothing, reload the page, then simply repeat until they drop something. Golden/Wrath cookies from a Cookie Storm or Cookie Chain also can unlock eggs. Thus, summoning Cookie Storms with Dragon Orbs in Grandmapocalypse are by far one of the fastest ways to get eggs (as Wrath Cookies have a higher chance of giving Cookie Storm and Cookie Chain as compared to Golden Cookies). It is also possible to export during a Cookie Storm and import if not all useful eggs are unlocked.
Egg Unlock Probabilities
When an egg is generated, there is a 10% chance for it to be a rare egg, otherwise it is a common egg.
If the generated egg has already been unlocked, then a second egg is generated. This reduces, but does not nullify, the effect the number of already unlocked eggs has on your chances of finding new eggs. Having more eggs reduces the chance of you finding other eggs quadratically.
The probabilities of generating a new egg, a common egg, any rare egg, or a specific rare egg (e.g. omelette) can be calculated using the following formulas, where n is the number of normal eggs already unlocked, and r is the number of rare eggs already unlocked:
 Pr(new egg)
Exact values may be calculated here.
 Pr(common)
Exact values may be calculated here.
 Pr(any rare)
Exact values may be calculated here.
 Pr(specific rare)
Exact values may be calculated here.
Average Unlock Time
If we unlock easter eggs using only Golden Cookies, the average number of Golden Cookie clicks required to unlock all easter eggs can be calculated. The calculation includes the effects of unlocking the Omelette egg (whenever it spawns naturally). Therefore, please ignore omelette factor when calculate the fail rate in this section.
The result curve is very similar to Lognormal distribution. For each fail rate we may fit the probability curve to Lognormal distribution to find the parameter μ and σ. Then we can use the formula on Wikipedia to obtain the probability we want.
For example, at fail rate 0.9, if you clicked or popped 753 objects, then there is 50% chance to collect all Easter eggs.
fail rate  50%  75%  95%  98%  Lognormal distribution  

μ  σ  
0.98  2351  3524  6310  8066  7.7625  0.6003 
0.97  1755  2515  4218  5245  7.4704  0.5330 
0.96  1437  2005  3241  3967  7.2700  0.4946 
0.95  1231  1691  2670  3236  7.1157  0.4706 
0.94  1085  1474  2291  2759  6.9890  0.4546 
0.93  973  1313  2019  2420  6.8808  0.4435 
0.92  885  1188  1812  2166  6.7858  0.4356 
0.91  813  1087  1649  1966  6.7009  0.4298 
0.9  753  1003  1516  1804  6.6240  0.4254 
0.875  637  845  1269  1506  6.4575  0.4185 
0.85  554  733  1096  1299  6.3176  0.4148 
0.825  491  649  968  1146  6.1965  0.4128 
0.8  441  582  868  1027  6.0895  0.4116 
0.75  367  485  722  854  5.9062  0.4108 
0.7  315  416  619  732  5.7526  0.4106 
0.6  246  324  483  571  5.5034  0.4110 
0.5  201  266  396  469  5.3050  0.4113 
0.3  148  196  291  345  4.9982  0.4112 
Achievements
Icon  Name  Description  ID 

The hunt is on ^{[note 5]}  Unlock 1 egg.  166  
Egging on ^{[note 5]}  Unlock 7 eggs.  167  
Mass Easteria ^{[note 5]}  Unlock 14 eggs.  168  
Hide & seek champion ^{[note 5]}  Unlock all the eggs. Owning this achievement makes eggs drop more frequently in future playthroughs. 
169 
Gallery
This season is one of two seasons to have its own grandma form, the bunny grandma. The other is the Christmas Season.
Notes
 ↑ Upgrades which lower the cost of upgrades stack multiplicatively, not additively. That is, if you have 3 of them which reduce the cost of upgrades by 5%, 2% and 1% then the final cost of an upgrade is (original cost) * 0.95 * 0.98 * 0.99.
 ↑ Multiplies bank by 1.05, cost activates before cookie gain. To optimize, save this upgrade until the end of a run then sell all buildings with Earth Shatterer and Reality Bending before buying this upgrade.
 ↑ The formula for CpS boost is:
 where , and "days" is the current session's length.
 ↑ "egg" is the only upgrade in the game that gives a flat CpS increase (only upgrade that doesn't increase CpS by a percentage.)
 ↑ ^{5.0} ^{5.1} ^{5.2} ^{5.3} The eggs only need to be found for the achievements to be earned, they do not need to be purchased. This allows the Chocolate Egg to count towards progress without having to purchase it for its onetime effect, such that it can be saved for later.
Trivia
 The description of the upgrade "Duck Egg" is a reference to a popular YouTube video, "The Duck Song."
 The Chicken Egg's flavor text references the classic dilemma of whether the chicken or the egg came first.
 The omelette's flavor text is a reference to the "omelette du fromage" episode of Dexter's Laboratory.
 The salmon roe flavor text is a reference to a song in the anime Tengen Toppa Gurren Lagann.
 The Century egg is an ingredient in Chinese cuisine, while the flavour text is a reference to the Discworld novel Interesting Times.
 The Shark egg's description is from the thoughts of sharks in one of Orteil's other games, Nested. It is possibly also a reference to the sharks from the Pixar film "Finding Nemo".
 The Bunny Grandma bears a striking resemblance to Frank, a character from the 2001 film 'Donnie Darko'.
 The robin egg's flavor text is a reference to the catchphrase of Robin from the 1960s Batman TV Series.
 The Golden Goose Egg's flavor text is a reference to Jack and the Beanstalk, as well as a related idiom: "killing the goose that laid the golden eggs."
 The Bunny biscuit text is a reference to one of the rabbit myths told in Watership Down.
 The "egg" bears a strong resemblance to Yoshi's eggs from Super Mario World and a normal Pokémon egg from the game series "Pokémon". It may also be a reference to the glitch pokemon "Egg". This pattern is also similar to a default spawn egg from Minecraft.
 Orteil said that the flavor text for "egg" is neither a pun nor a reference. However, in French, "an egg" is pronounced "un œuf" which sounds exactly like "neuf" = 9.
 Mass Easteria is probably a reference to mass hysteria, also called mass psychogenic illness.
 
 
 
 
 
