How Many Days to Walk The Routeburn Track?

Which direction to walk?
Walking from RTB Roadend end to Divide. This is the most popular direction, maybe due to the fact that most of the track guides are written in this direction.

Start at Divide. This is the preferred direction for day walkers and runners. Overall this direction has less height gain than starting at RTB Roadend.

Option 1. 4 Nights 5 Days.
Immerse yourself and stay a night at each hut. This is the preferred option when you have no time constraints. This gives you plenty of time to explore the various side tracks as well.

Option 2. 3 Nights 4 Days. (depending on Hut availability)
Overnight at Routeburn Flats, Routeburn Falls, Lake MacKenzie.
Allows for time to explore the Routeburn North Branch and Viewpoint above Falls Hut.
Overnight at Routeburn Falls, Lake MacKenzie, Lake Howden.
Make the most of all the major viewpoint side trips.
Overnight at Routeburn Flats, Routeburn Falls, Lake Howden.
Have a good rest and a bite to eat at Lake MacKenzie before carrying on. Leave early (8am) if hiking from Lake Howden to Falls.
Overnight at Routeburn Flats, Lake MacKenzie, Lake Howden.
Have an early start (8am) from Flats or MacKenzie to allow yourself plenty of time to enjoy the sights.

Option 3. 2 nights 3 days. (depending on Hut Availability.) This is the most popular time frame.
Overnight at Routeburn Falls and Lake MacKenzie. (Either way)
Most popular choice making for 3 days of hiking with the similar energy required. Good viewpoints on each day, so if the weather is bad one day you still have a chance of seeing views on another day.
Overnight at Routeburn Flats and Lake Mackenzie. (Either way)
Enjoy the peace and quiet at Flats. Most popular choice for Campers.
Overnight at Routeburn Falls and then Lake Howden.
Overnight at Routeburn Flats and then Lake Howden.
Have an early start (8am). Stop at Lake Mackenzie for a good rest and a bite to eat. Most hikers tend to get very tired once they leave Lake Mackenzie and enter the bush with its uphill section.
Overnight at Lake Howden and Routeburn Falls
Overnight at Lake Howden and Routeburn Flats.
Have an early start. Have a good rest, bite to eat and drink at Harris Saddle Shelter. The walk downhill from Harris Saddle can be just as hard then going uphill when you're tired.

Option 4. 1 night 2 days.
Overnight at Routeburn Falls
Overnight at Lake MacKenzie.
Depending on which end you start, both of these options will have 1 normal day and 1 Long day.
Overnight at Routeburn Flats.
Overnight at Lake Howden.
For these possibilities: 1 Short day and 1 Long day (depending on which end you start)
On your long day (10hrs+) have an early start so that you have plenty of time to reach the end before dark. Stop at each hut along the way, have a good rest, a bite to eat and a drink. Walk at a comfortable but continuous pace to maximise your energy use. Ensure you have the fitness to do this before starting.

1 Night 2 Days vs 1 Day Walk
If you can book a night at either Routeburn Falls or Lake MacKenzie then staying overnight and taking 2 days is the preferred option. However, if you can only get a booking at Routeburn Flats or Lake Howden then I would consider walking the track in One Day. When staying at Flats or Howden you will have one short day and one very long day 10hrs-12hrs with a full pack, whereas walking the complete track with a day pack will also take 10-12 hrs. 10hrs with a day pack is easier than 10hrs with a full pack. The day walk gives you more of an option to walk the track when the weather is more suitable.

Option 5. 1 Day Walk
Why start at Divide. Overall there is less height gain this way. The hard part of the track is in the first half. After Harris Saddle it's all down hill and the terrain becomes easier the closer you get to the RTB Roadend.
If you're planning on doing the Routeburn in a day average time is 10-12hrs with only short rests along the way. So start early and ensure that you have the physical fitness to walk the 32km of Alpine terrain.

Option 6. 1 Day Run
Why start at Divide. This is the same direction as the Routeburn Classic running race in mid-April.
(otherwise same reasons as for walking). Most first time RTB runners aim to finish in under 5hr.
How Fast is Fast. On April 22nd, 2017 Jack Beaumont from Queenstown set a new Routeburn Classic record. 2 hrs 37 mins 51 secs.

For an excellent article on running The Routeburn Track written by respected Trail Runner Sarah Lavender Smith.