This article is an excerpt from the Shortform summary of "Expecting Better" by Emily Oster. Shortform has the world's best summaries of books you should be reading.
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What are your chances of getting pregnant, depending on the day that you ovulate?
The good news is, your chances of getting pregnant are pretty good, ranging from 10 to 35%, depending on when you try conceiving relative to your ovulation day. However, outside of a range of days, you have 0% chance of getting pregnant.
We’ll cover how ovulation works, your specific chances of conception before ovulation, and why the chance of getting pregnant varies so much.
Brief Intro to Ovulation
The ovulation cycle lasts 28 days on average. Starting from Day 1, when the period starts, the first 14 days are gearing up for ovulation. On Day 14, the egg is released and travels through the Fallopian tube toward the uterus. This journey takes around 6 days. If the egg is fertilized, it implants in the uterus around Day 23.
Critically, the egg survives only an average of 24 hours, well before it makes it to the uterus. Therefore sperm must be waiting around in the Fallopian tube, right as the egg is released.
Luckily, sperm live up to 5 days in the Fallopian tube. Therefore, the best chance of conception happens the day before or the day of ovulation. Conception can still happen up to 5 days before ovulation, with lower chances.
Chances of Getting Pregnant Before Ovulation
Here’s a graph of chances of conception depending on the day of the ovulation cycle, in women aged 26-35. Day 14 is the day of ovulation. so Day 9 is 5 days before ovulation.
Just to make this very clear, here are the chances in a table:
| Chances of Getting Pregnant 6 Days Before Ovulation | 0% |
| Chances of Getting Pregnant 5 Days Before Ovulation | 10% |
| Chances of Getting Pregnant 4 Days Before Ovulation | 15% |
| Chances of Getting Pregnant 3 Days Before Ovulation | 13% |
| Chances of Getting Pregnant 2 Days Before Ovulation | 26% |
| Chances of Getting Pregnant 1 Days Before Ovulation | 31% |
| Chances of Getting Pregnant On Ovulation Day | 32% |
| Chances of Getting Pregnant 1 Day After Ovulation | 0% |
Myth: It’s best to have sex every other day, so you can hit at least one of the two best days and save up your sperm.
Reality: Chances of conception are nearly identical whether you have sex once, twice, three times, or more in the 6-day window before ovulation. The critical thing is to hit the day of ovulation or the day before.
Fun fact: Out of say ~500 million sperm in an ejaculation, only 200 will reach the egg and have a chance of fertilization.
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Here's what you'll find in our full Expecting Better summary :
- Why much parenting advice you hear is confusing or nonsense
- The most reliable way to conceive successfully
- How much alcohol research shows you can drink safely while pregnant (it's more than zero)
- The best foods to eat, and what foods you really should avoid
