When should I weigh myself before starting a diet if I am a woman?

Women tend to retain much more water just before their periods. Be sure to take this into account when you start your diet and take measurements. Ignore scale readings in the 10 days before menstruation. Treat your first weighing following your period (as soon as one day following is fine) as your "after" measurement. Don't let short-term water fluctuations discourage you. Be aware of your menstrual timing so you don't mistakenly conclude the diet isn't working.