That's an increase of about 116,000 passengers.
The Calgary-based airline says it had a load factor of 82.3 per cent, down from 82.7 per cent in the same month last year.
Its passenger traffic increased 6.5 per cent year-over-year. Capacity grew 7.1 per cent year-over-year to 2.15 billion available seat miles.
WestJet releases its first-quarter financial results on Tuesday.
The airline has said half the anticipated growth this year will come from its Encore regional service.
WestJet expects to take delivery of eight Q400s this year, doubling its fleet to 16 as it expands service from Toronto.