Norwegian carried almost 3.5 million passengers in June as capacity grew by 43%.
The Scandinavian low-cost carrier, subject to takeover interest from International Airlines Group and Lufthansa, saw carryings improve by 14% year-on-year.
The load factor edged up by 0.8 percentage points to 90.5%.
Chief executive Bjørn Kjos said: “Our capacity growth is still high, but it is not increasing as rapidly as previous months, which is in line with our strategy.
“We have been through a long period of strong growth and going forward we will reap what we have sown for the benefit of our customers, staff and shareholders.”
The third largest airline at Gatwick took delivery of one Boeing 787-9 Dreamliner and one Boeing 737 MAX 8 last month.