Probability of Conception by Month

thelaststraw05

I thought I'd share this from a conversation going on over on the TTGP board (http://community.thebump.com/cs/ks/forums/thread/67042809.aspx).

I'm a bit of a math guy and I like knowing specific probabilities. TTC has a specific probability around 20% each month.

What this means is that if 1000 healthy couples tried to conceive any given month, 200 of them would get pregnant. Of the 800 remaining couples 160 will get pregnant the next cycle. Of the 640 remaining couples, 128 will get pregnant the next cycle.

More formally, the math works out like this:

[Cumulative Chance of a BFP for a "Health Couple"] = 1-(80%)^[Number of Months TTC]

Month -- Cumulative Chance -- % of Couple w/ BFP this month

1        --           20.00%        --           20.00%
2        --           36.00%        --           16.00%
3        --           48.80%        --           12.80%
4        --           59.04%        --           10.24%
5        --           67.23%        --             8.19%
6        --           73.79%        --             6.55%
7        --           79.03%        --             5.24%
8        --           83.22%        --             4.19%
9        --           86.58%        --             3.36%
10      --           89.26%        --             2.68%
11      --           91.41%        --             2.15%
12      --           93.13%        --             1.72%

If you are just starting TTC now, you can take some comfort that 50% or so of couples will be pregnant after just 3 months. If you have been TTC for a while, you can take solace in the fact that 1-in-20 health couples is still not pregnant after a year (you aren't alone).