Central is always exactly one hour behind
Of all the American zone pairs this is the easy one. Eastern and Central sit on adjacent hours and, crucially, they change their clocks on the same two Sundays each year. Whatever the season, the gap stays at one hour: 10:00 AM in New York is 9:00 AM in Chicago in January and in July alike. You never have to work out which side has switched.
EST or EDT — it changes the label, not the gap
Between the second Sunday in March and the first Sunday in November, Eastern is on EDT and Central is on CDT. Outside that window they are EST and CST. Both labels shift together, so a message reading “3 PM EST” sent in July is loose wording rather than a real error here: the sender means Eastern local time, and 2 PM Central is right either way. This is the one pair where the usual EST-versus-EDT trap costs you nothing.
The states that are split down the middle
The zone line does not follow state borders. Tennessee, Kentucky, Florida, Indiana, Michigan and a handful of others straddle it. Nashville is Central while Knoxville is Eastern. Most of Indiana is Eastern, but several counties near Chicago and Evansville run on Central. The Florida panhandle west of the Apalachicola River is Central while Miami is Eastern. If a colleague is in one of those states, ask for their city rather than assuming from the state name.
Practical scheduling
A 9-to-5 workday in Chicago is 10-to-6 in New York, so the overlap is almost total. The friction is at the edges: an 8:00 AM Eastern standup is 7:00 AM in Chicago, and a 5:00 PM Central deadline has already passed 6:00 PM on the East Coast. For anything with a cut-off, write the zone next to the hour.