That is a complicated question, the answer will depend on what army, its composition, where it's marching, when, the size, and lastly sources for water.

Addressing the first, a professional army (e.g. Roman or Macedonian) will likely be organized and better disciplined. They may have engineers to repair/clear roads for faster travel by the army - essential if they have a large supply column.

Is the army primarily cavalry or mostly infantry? Is it a raiding column or an army marching with its siege train? Is it moving through friendly territory which negates the need to construct a marching camp each day (which would cut into the marching time)?

If it's during the winter months with shorter days then you'll have fewer hours of daylight to march in.

The larger the army the slower it will move. If you've a massive army, it could take an hour (or more) for the rear of the column to start moving after the vanguard started marching. Your marching day is constrained by the time the rear of the column reaches camp - because those in the rear still need enough light time to setup their tents, get firewood and water and then cook a meal.

Lastly, sources for water will limit your day's march. If your next source is only 8 miles away and the next after that is 15 miles, then you're likely only going to manage a short distance.

Taking a look at Alexander's march into Asia, his speed varied from 10.5mpd to 19.5mpd. When he had a cavalry only force he could hit distances of ca. 46mpd.

hi! you may be interested in some related threads

• We all hear about how ancient armies marched for months across huge distances for battle. Truly what was this like and how fast could they march?

• How long does it take a Roman army from Rome to march to Paris? its about 1100 km. takes about 24 hrs to walk 100 km. so about ? so about 22 days ?

• How Far Could a Medieval Army Move Per Day?

• How fast/far could an army travel in Medieval Europe?

edit: added Roman post