When comparing two dates, what term is best used to say that one should come before the other?

For example, a user of my application can input two dates, that form a time interval. Obviously the "start date" has to be a valid date that comes *before* the "end date", so when the user enters these wrong I show him an error message. But, since English is not my native language, I don't know that comparison term to use. 

Can a date be said to be *"smaller"* than another date? Or should I use something like *"anterior"*, or *"earlier"*?