The Shettles method, step by step
Dr Landrum Shettles set out the method in the 1970 book How to Choose the Sex of Your Baby. It rests on the idea that sperm carrying a Y chromosome (boy) swim faster but die sooner, while sperm carrying an X chromosome (girl) are slower but last longer. The calculator turns his timing rules into dates:
- For a girl: sex as often as you like after your period, with the last time two to four days before ovulation. Then no sex until two days after ovulation, so no sperm are waiting when the egg is released.
- For a boy: no sex from the start of the fertile window until ovulation day, then sex on ovulation day and the day after, so the faster Y sperm reach the egg first.
Everything depends on knowing your ovulation day. A calendar estimate assumes ovulation 14 days before your next period, which is often a day or more off. A positive LH test is closer: ovulation usually follows within 24 to 36 hours.
Does the Shettles method work?
The best evidence says no. Wilcox and colleagues followed 221 women who recorded intercourse daily while urine hormones pinned down their ovulation day. Of the babies born, the share of boys was the same whether conception followed sex days before ovulation or on the day itself. An earlier prospective study by France and colleagues, and a 1991 review of natural sex-selection methods, also found no support for the timing. Laboratory work has not found the differences in speed or survival between X and Y sperm that the method assumes.
Following the girl plan has a real cost: it skips the two days most likely to start a pregnancy, so it can add months to trying. The boy plan is harmless for conceiving, but the abstinence before ovulation day is not needed. If what you want is a baby, the best time to get pregnant calculator gives the days that matter, and an ovulation test calculator tells you when to start testing.
Frequently asked questions
How do you calculate the Shettles method?
Find your ovulation day first, either from your calendar (the day about 14 days before your next period is due) or as the day after your first positive LH test. For a girl, the method says have sex up to two to four days before ovulation, then stop until two days after it. For a boy, it says abstain until ovulation day, then have sex on ovulation day and the day after.
What is the Shettles method success rate?
Shettles claimed success rates of 75% or more, but those figures came from his own patients without a control group. Studies that recorded the timing of intercourse precisely found no link with the baby's sex: in the Wilcox 1995 study, the share of boys was the same whichever day conception happened. In practice the chance of a boy stays about 51% either way.
How many days before ovulation should you stop for a girl?
The Shettles method says the last time should be two to three days before ovulation, with some versions allowing up to four. That means skipping the day before ovulation and ovulation day itself, which are the two days most likely to lead to a pregnancy, so following it usually takes longer to conceive.
Should I use ovulation tests with the Shettles method?
For the boy timing, a positive LH test is the most practical signal, because ovulation usually follows within 24 to 36 hours. For the girl timing, a test is less useful: by the time it turns positive, the method's girl days have already passed. The calculator then plans your next cycle from that positive day.
Do Shettles positions, diet or douching make a difference?
No. Shettles' book also recommends deep or shallow penetration, vinegar or baking soda douches, and timing of orgasm to change vaginal pH. None of these has been shown to change the sex of a baby, and douching can irritate the vagina and raise the risk of infection, so it is best avoided.
Sources
- Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby (Wilcox, Weinberg, Baird) - New England Journal of Medicine, via PubMed, 1995-12-07.
- A prospective study of the preselection of the sex of offspring by timing intercourse relative to ovulation (France et al.) - Fertility and Sterility, via PubMed, 1984-06.
- Natural family planning and sex selection: fact or fiction? (Gray) - American Journal of Obstetrics and Gynecology, via PubMed, 1991-12.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.