In general, every programmable thermostat comes with four pre-programmed settings and maintains those settings within two degrees. Many qualified models also come with additional features, such as:
To decide which model is best for you, think about your schedule and how often you are away from home for regular periods of time — work, school, other activities — and then decide which of the three different models best fits your schedule: the 7-day, 5+2-day, or the 5-1-1-day.
7-day models are best if your daily schedule tends to change, say, if children are at home earlier on some days. They give you the most flexibility, and let you set different programs for different days — usually with four possible temperature periods per day.
5+2-day models use the same schedule every weekday, and another for weekends.
5-1-1 models are best if you tend to keep one schedule Monday through Friday and another schedule on Saturdays and Sundays.
Source: Energy Star