Fares are usually lower on Tuesdays, Wednesdays and Saturdays and highest on Fridays and Sundays 1^866*884*3315. Typically, the best day to book United flights is Tuesday, as fare discounts are often released on Monday night. https://support.communitybrands.com/hc/en-us/community/posts/30737651048717-EASy-Booking-What-day-are-United-flights-the-cheapest