Can you really do Banff in a day from Calgary? Yes, and plenty of people do. You will not see everything, and you should not try to. What works is picking three or four things you care about, leaving early and letting someone else handle the driving and parking. Here is a realistic plan.

The drive is around an hour and a half each way in decent conditions, so you spend three hours in the car and about ten hours in the park if you go early and come back in the evening. Leave Calgary around seven, and you are in the Bow Valley while the mountains still have that pink edge. That head start matters. By midday Banff Avenue is busy, and parking in town is tight.
7:00 a.m. Leave Calgary. Take coffee for the road. The last stretch into the Rockies is when people usually put their phones down and stare out the window.
9:00 a.m. Bow Falls and Surprise Corner. A short walk by the river, with the Fairmont Banff Springs hotel up the slope. It is easy, scenic and a gentle start.
10:00 a.m. Banff Gondola. The ride up Sulphur Mountain gives you a wide view of the valley and the town below. Book timed entry if the operator offers it, and check the weather first; a cloudy day gives you a lot less for the ticket.

12:30 p.m. Lunch on Banff Avenue. There are enough places to suit most budgets. Leave time to wander, because the shops and side streets are part of the draw.
2:00 p.m. Lake Minnewanka or the Vermilion Lakes. Minnewanka is a larger lake a few minutes outside town and good for a walk along the shore. The Vermilion Lakes are quieter, best around sunset, and a favourite with photographers.
4:30 p.m. Optional extra. If you still have energy, this is the slot for Cave and Basin National Historic Site or a drive along the Bow Valley Parkway. Check Parks Canada before you go for current closures and seasonal restrictions, since some trails and roads change with the year.
6:00 p.m. Dinner, then head home. Allow time for a relaxed meal. The road back is calmer than the morning, and most of your group will be asleep by Canmore.
You get to look at the scenery, enjoy a glass of wine at dinner and not worry about the drive back in the dark. The vehicle is yours for the day, so luggage, jackets and shopping bags stay in the car. It also means the plan can flex. If the Gondola is in cloud you swap it for something else without stressing about a rental return time.
Our Calgary to Banff private tour and the main Banff limo service are set up for exactly this. If you want a longer stay, see our itineraries for 3 days, 5 days and 10 days. For a one-day plan built around your group, get in touch.
Yes, if you leave early and pick a few highlights. It is a long day, but entirely doable.
About an hour and a half each way in normal conditions.
Generally yes for time spent in the national park. Check Parks Canada for current requirements before you go.