# Let's see how many days of the year we can fill with Doper Birthdays. **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [October 7, 2005, 9:47pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244 "2005-10-07T21:47:32Z")\ **Posts on this page:** 20\ **Page:** 17
**Author:** ![Critical\_Mass](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@Critical\_Mass](https://boards.straightdope.com/u/Critical_Mass)\ **Post date:** [October 12, 2005, 1:10am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/321 "2005-10-12T01:10:34Z")
Add me for March 2 ---
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [October 12, 2005, 1:20am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/322 "2005-10-12T01:20:43Z")
New Year’s baby. December 31. ---
**Author:** ![Marathon](https://avatars.discourse-cdn.com/v4/letter/m/7cd45c/32.png) [@Marathon](https://boards.straightdope.com/u/Marathon)\ **Post date:** [October 12, 2005, 1:25am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/323 "2005-10-12T01:25:21Z")
You can add me for January 27th (Mozart’s bday, too!) ---
**Author:** ![furlibusea](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@furlibusea](https://boards.straightdope.com/u/furlibusea)\ **Post date:** [October 12, 2005, 1:25am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/324 "2005-10-12T01:25:39Z")
December 21st ---
**Author:** ![sleeepy2](https://avatars.discourse-cdn.com/v4/letter/s/e9a140/32.png) [@sleeepy2](https://boards.straightdope.com/u/sleeepy2)\ **Post date:** [October 12, 2005, 1:32am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/325 "2005-10-12T01:32:40Z")
October 21 ---
**Author:** ![Elmo\_Lincoln](https://avatars.discourse-cdn.com/v4/letter/e/5f8ce5/32.png) [@Elmo\_Lincoln](https://boards.straightdope.com/u/Elmo_Lincoln)\ **Post date:** [October 12, 2005, 2:42am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/326 "2005-10-12T02:42:32Z")
April 10 for Elmo Lincoln ---
**Author:** ![Sternvogel](https://avatars.discourse-cdn.com/v4/letter/s/bc79bd/32.png) [@Sternvogel](https://boards.straightdope.com/u/Sternvogel)\ **Post date:** [October 12, 2005, 2:53am UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/327 "2005-10-12T02:53:08Z")
> [@marque elf](#): > > Statistically it supposedly works out that in any group of 30 people, 2 will have the same birthdate. … Can any explain to me why this is so? [Here is a site which explains the birthday problem.](http://www.studyworksonline.com/cda/content/explorations/0,,NAV2-76_SEP949,00.shtml) ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [October 12, 2005, 12:37pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/328 "2005-10-12T12:37:17Z")
> [@Sean Factotum](#): > > Well **May 9th** is still open as of the last update, so I’ll claim that. Damn you. Is there room on that day for the two of us? ---
**Author:** ![kittenblue](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@kittenblue](https://boards.straightdope.com/u/kittenblue)\ **Post date:** [October 12, 2005, 12:40pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/329 "2005-10-12T12:40:35Z")
March 6 ---
**Author:** ![One\_And\_Only\_Wanderers](https://avatars.discourse-cdn.com/v4/letter/o/838e76/32.png) [@One\_And\_Only\_Wanderers](https://boards.straightdope.com/u/One_And_Only_Wanderers)\ **Post date:** [October 12, 2005, 12:54pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/330 "2005-10-12T12:54:22Z")
Feb 10th. Woohoo it hasn’t gone yet. I thought I would have to share for sure by now. ---
**Author:** ![Noone\_Special](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/noone_special/32/2863_2.png) [@Noone\_Special](https://boards.straightdope.com/u/Noone_Special)\ **Post date:** [October 12, 2005, 1:24pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/331 "2005-10-12T13:24:19Z")
> [@hajario](#): > > Not exactly. If you have a group of 23 people, it is more likely than not that at least two of the 23 have the same birthday. The easiest way to calculate this is to take 23 people and calculate the odds that none of the 23 have the same birthday. My stats book is too dusty and in a way to inconvenient place for me to do anything but leave the rest as an exercise to the reader. OK, let’s run through this in a bit more detail… 1 guy – any of 365 days (let’s leave Feb 29 out of this for the moment). His “chance” of not “sharing” his birthday is 365/365, or 100%. Chance that **2[sup]nd[/sup]** guy **does not** share birthday with first is 1 - 1/365, or 364/365. Chance that 3[sup]rd[/sup] person does not share a birthday with first two, **assuing the first two were born on different days** , is 363/365. Now comes the hard part – the chance that #2 doesn’t share with #1 **and** #3 shares with neither is (364/365)_(363/365); which is still darn close to 1. (this should technically be prefixed by "(365/365)_" for the first person, but let’s not be silly…) For the 23 rd person, the chance of having no shared birthday is (364/365)_(363/365)_(362/365)_…_((365-22)/365). Or - (364_363_362\*…\*343)/(365^22). Now it turns out the result of this calculation is 0.4927…, or just about 50%. So the 23[sup]rd[/sup] person in a random sample has a 50/50 chance of sharing a birthday with one of the other 22. ---
**Author:** ![surrotobeinMD](https://avatars.discourse-cdn.com/v4/letter/s/6a8cbe/32.png) [@surrotobeinMD](https://boards.straightdope.com/u/surrotobeinMD)\ **Post date:** [October 12, 2005, 1:34pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/332 "2005-10-12T13:34:34Z")
August 19th ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [October 12, 2005, 1:40pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/333 "2005-10-12T13:40:24Z")
> [@marque elf](#): > > Statistically it supposedly works out that in any group of 30 people, 2 will have the same birthdate. The first place I heard this was _Let’s Make A Deal_, perhaps not the most reliable of sources. Later I heard from a more reliable source. I never took statistics so I wouldn’t understand the math but intuitively this doesn’t seem right to me. Your odds for any specific birthday are only 1 in 365/366. Why does the probability drop down to 1 in 1 when 30 people are present? Each birthday is a random event. Shouldn’t then the probability be 1 in 365 times 2 times 30? That doesn’t equal 1 in my book. > > Can any explain to me why this is so? As people have pointed out, it’s not guaranteed that 2 will have the same birthday… it’s just a better than 50/50 proposition to take. And, try thinking of it this way. Have your 30 people all shake hands, each person with every other person, and say their birthdays as they do so. Each person has to shake hands with 29 other people. Since there are two people involved in each handshake, that means (30 \* 29) / 2 or 435 distinct handshakes. In each of those handshakes, there is a 1/365 probability that they will say the same birthday… (slightly less considering that there might be a leap baby in the group, slightly more if you allow for slight annual fluctuations in the birth rate.) From here on the math gets complicated, but it’s not too surprising that you have a fairly high probability of a match among those 435 distinct pairs. Hope that helped. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [October 12, 2005, 1:46pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/334 "2005-10-12T13:46:20Z")
> [@marque elf](#): > > We have had 206 respondents for 160 days. That may not equal 1 in 365 but it is not far off from it either. Not quite sure what you mean here… we’ve had over 40 collisions in a group of 200-some people, that’s a little outside the scope of the birthday paradox but it seems to support it. And, keep in mind, there was a selection bias AGAINST people posting if they spotted someone already having their birthday (I think) because the OP was asking for people to try to ‘fill up days in the calendar’. If your day is already filled, then you’re not helping to accomplish that goal, though you do have a chance to say hi to someone else who shares your birthday. ---
**Author:** ![Theodore\_Striker](https://avatars.discourse-cdn.com/v4/letter/t/74df32/32.png) [@Theodore\_Striker](https://boards.straightdope.com/u/Theodore_Striker)\ **Post date:** [October 12, 2005, 2:05pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/335 "2005-10-12T14:05:38Z")
March 28th- that should knock another one out. ---
**Author:** ![Staggerlee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/staggerlee/32/3134_2.png) [@Staggerlee](https://boards.straightdope.com/u/Staggerlee)\ **Post date:** [October 12, 2005, 2:07pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/336 "2005-10-12T14:07:30Z")
2nd January for me, please. ---
**Author:** ![dasgupta](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@dasgupta](https://boards.straightdope.com/u/dasgupta)\ **Post date:** [October 12, 2005, 5:50pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/337 "2005-10-12T17:50:38Z")
Looks like I’m the third October 16[sup]th[/sup]. ---
**Author:** ![Idle\_Thoughts](https://avatars.discourse-cdn.com/v4/letter/i/838e76/32.png) [@Idle\_Thoughts](https://boards.straightdope.com/u/Idle_Thoughts)\ **Post date:** [October 12, 2005, 10:08pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/338 "2005-10-12T22:08:35Z")
> [@marque elf](#): > > We have had 206 respondents for 160 days. That may not equal 1 in 365 but it is not far off from it either. Don’t know if anyone answered this yet–when I update I read the replies one at a time, so I haven’t seen any reply after this yet–But 206 is actually the number of days we have represented. Not the number of people in here who gave me their birthday. 160 is the number of days still left that nobody has “claimed” yet. ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [October 12, 2005, 10:18pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/339 "2005-10-12T22:18:54Z")
June 24th here. Hubby is April 8th ---
**Author:** ![Idle\_Thoughts](https://avatars.discourse-cdn.com/v4/letter/i/838e76/32.png) [@Idle\_Thoughts](https://boards.straightdope.com/u/Idle_Thoughts)\ **Post date:** [October 12, 2005, 10:25pm UTC](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244/340 "2005-10-12T22:25:46Z")
> [@chrisk](#): > > And, keep in mind, there was a selection bias AGAINST people posting if they spotted someone already having their birthday (I think) because the OP was asking for people to try to ‘fill up days in the calendar’. If your day is already filled, then you’re not helping to accomplish that goal, though you do have a chance to say hi to someone else who shares your birthday. Yeah, tell me about it. See, this is what I was worried about and keep thinking every now and again. That people will come in and see that their day is already “taken” and therefore not reply. I would hope they wouldn’t do that, because their day could count for the “Random Stats” and change those…but I can’t force people to reply if they don’t want to. 😛 All I can do is make this post. If you’re reading right now, or have already and are now just following along, and your birthday was already listed…so what? Reply anyway and be added to the number and say hi to the people who share it. 🙂 **Random Stats:** **Day with the most birthdays so far:** July 29th has 5 **Month with the most birthdays so far:** July has 31 **Month with the least birthdays so far:** April only has 18 **Number of days of the year so far:** 217 **Number of days still needed:** 149 **Biggest “run” in a row so far:** 9 (December 11th - 19th) _January_ 1st- Athena, supervenusfreak, Nancarrow 2nd- Staggerlee 3rd- BlackKnight, Madd Maxx 5th- Honey 6th- Ravenman 9th- Small Clanger 13th- A.R. Cane 14th- Diceman 18th- saramamalana 19th- DiosaBellissima 20th- NurseCarmen 21st- ladyfoxfyre, gommsn 23th- dalej42 25th- Rhiannon8404 27th- Barrytown 29th- Governor Quinn, Elza B. _February_ 2nd- Happy Lendervedder 3rd- Mona Lott 4th- romansperson 5th- Hampshire 7th- Hal Briston 8th- The Sausage Creature 10th- One And Only Wanderers 11th- coop 12th- percypercy 13th- Rhythmdvl 14th- Cat Jones 16th- Aholibah 17th- Little Bird 19th- Enright3 20th- mikeargo 21st- stargazer 22nd- OliverTwistofLime, Jackknifed Juggernaut 23rd- ryobserver 25th- Craneop2 28th- Stillwell Angel _March_ 1st- Kyyrewyyoae 2nd- qwest 4th- FilmGeek 6th- kittenblue 7th- The Mad Hermit 8th- Sierra Indigo 11th- faithfool 12th- LoganDear 14th- straykat23 15th- TwoTrouts 16th- nonacetone, Jennshark 19th- Nymphadora, AuntiePam 20th- metj 22nd- CWN 24th- Mrs. Franchi 25th- Cerri 28th- Theodore Striker 29th- ultrafilter 30th- Brilharma 31st- Rockwell, MrsMonkey _April_ 1st- Astroboy14 5th- wolfstu 10th- SeeNoReason, elfkin477, Elmo Lincoln 11th- Waenara, Buckler of Swashing 12th- brightpenny 16th- Susie Derkins, Penchan, irishgirl 20th- AngelicGemma 23rd- BayleDomon 24th- jsgoddess 25th- percussion 26th- runner pat 28th- BrattiAtti, ZipperJJ _May_ 1st- Avarie537, PinkMarabou 3rd- chimichanga 6th- sneezy5660, Jpeg Jones 9th- Sean Factotum, Uncommon Sense 10th- Khadro, ladybug 11th- ErinPuff 12th- Art Vandelay, Architect 14th- Good Egg 15th- Nic2004 16tg- Cub Mistress 18th- cher3 19th- Marley23 21st- robotic\_panda 24th- scr4 25th- Cunctator, MissTake 26th- LavenderBlue, Atheist Princess 27th- liberty3701 29th- Kilvert’s Pagan 31st- fruitbat _June_ 1st- ENugent, Ragiel 3rd- Miabella 2nd- Loach 4th- Demo 5th- sishoch 6th- Ponster 7th- Anastasaeon, Carm6773 8th- Cowgirl Jules 11th- mhendo 12th- Johnny L.A. 13th- Pixel 14th- Balle\_M 15th- Shagnasty 16th- Epimetheus 18th- GorillaMan 22nd- Inigo Montoya 23rd- Arwin 24th- Barracuda 25th- Long Time First Time 26th- 1920s Style “Death Ray”, hillbilly queen, MsRobyn _July_ 1st- newcrasher, photopat 2nd- Taran 5th- Starlite, trublmakr 6th- World Eater, Absolute, mkl12 10th- jsc1953 11th- pulykamell 12th- eleanorigby 14th- Enginerd, Waterman 15th- Landshark, ShibbOleth 16th- Antonius Block 17th- Mr. Goob 18th- Kythereia 19th- gfloyd 20th- Emilio Lizardo 23rd- MrFantsyPants 24th- Dung Beetle 29th- Ayesha, Bear\_Nenno, Ejs Girl, Kyla, Swambear 31st- Bird Man, Yeticus Rex, Vunderbob, krisolev _August_ 1st-moonstarssun, BraheSilver 2nd- Ninja Chick 3rd- Meaty Beaty Big and Bouncy, Mint Julep 4th- Suburban Plankton, Hokkaido Brit 8th- AntaresJB, pudytat72 10th- Ice Wolf 12th- Mighty Girl, Butterscotch 18th- psycat90 19th- Grasshopper, surrotobeinMD 21st- StarvingButStrong, Ludy, KJ 22nd- Hilarity N. Suze, akira5822 24th- Mr. Blue Sky 27th- Faruiza, Tamryne 28th- interface2x 30th- Sternvogel, cherry, Monstre 31st- VenusProbe _September_ 2nd- BitternessComesStandard 6th- bobkitty 8th- Lsura 9th- vivalostwages 12th- jrfranchi 13th- XWalrus2 14th- Johanna 16th- The Flying Dutchman, feppytweed 17th- Miss Violaceous 18th- WallFlower 20th- Canadiangirl, racer1 21st- Misnomer 23rd- Spikesbud 28th- TellMeI’mNotCrazy, Harimad-sol, Encinitas 29th- Crafter\_Man 30th- Blalron, anyrose _October_ 1st- Eleusis, fishbicycle 3rd- racer72 5th- Nutty Bunny 6th- Manatee, Otanx 7th- malkavia, ltfire 8th- LaurAnge 10th- danceswithcats, Ellen Cherry 11th- PaperBlob 12th- Stinkum 13th- slai 14th- Martha, August West 15th- Ms Macphisto 16th- BadBadger, Antigen, dasgupta 18th- Smashed Ice Cream 19th- Spongemom 21st- sleeep2 22nd- Hentor the Barbarian 26th- Gail 31st- seosamh, dangermom _November_ 2nd- Harborwolf 3rd- jackelope 4th- Sassy 5th- YaWanna 6th- BwanaBob 7th- melondeca 10th- movingfinger, norinew 11th- EvilAsh 13th- marque elf, Jman 14th- Voyager 16th- Pyroette 17th- chrisk 18th- UncaStuart 20th- cat39645 22nd- Idle Thoughts 23rd- BiblioCat 26th- KSO, WhyNot 27th- DirtyHippy, Odinoneeye 30th- Noone Special, infamousmom, Anaamika _December_ 1st- Khadaji, Marconi & Schmeese, CalMeacham 2nd- Snakescatlady 4th- Zeldar, Mishell 9th- Misery Loves Co. 11th- PookahMacPhellimey 12th- Rushgeekgirl, Twoflower 13th- betenoir 14th- Corporate Hippie 15th- Lady Venom 16th- csharpmajor 17th- mr bus guy, detop 18th- PinkNailFile 19th- Clothahump 21st- furlibusea 22nd- Pandora 23th- PigBoy 24th- dare\_devil007\_ 25th- Kat, Annie-Xmas 27th- MissGypsy 28th- amarone, picker 29th- dinahmoe 31st- Jake [Previous page](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244.md?page=16) [Next page](https://boards.straightdope.com/t/lets-see-how-many-days-of-the-year-we-can-fill-with-doper-birthdays/325244.md?page=18)