All Nippon Airways and Japan Airlines increased fuel surcharges Wednesday, with fees topping $400 on some long-haul flights. The hikes, which apply to tickets purchased in July and August, come even as jet-fuel rates in Asia are dropping. That's because Japan's two largest airlines calculate the fees based on averages that lag current prices by several months.

Jet fuel fell to $113 per barrel Wednesday, from a record high of $242 per barrel in late March, according to data from LSEG. But the surcharges that start this week are based on prices from April and May, which averaged $178.21, according to a JAL press release. Surcharges could have ballooned even higher without budget assistance from Japan's government to help with soaring energy prices resulting from the Iran war, the airline said.

Fuel levies on some routes have tripled since the start of the Iran war, with fees to fly to Japan from Hawaii, India and Indonesia jumping from $94 in April to $310 in July, according to ANA's website. JAL's surcharges are similar. The new levies top out at 65,000 yen for flights from North America (excluding Hawaii), Europe, the Middle East and Oceania.

That equates to around $400 after the yen hit a 40-year low against the greenback Tuesday. Fuel surcharges at ANA and Japan Airlines are revised on a bi-monthly basis. So, they're expected to drop for flights purchased in September and October, reflecting average jet fuel rates in June and July.

That could help travelers pay for other costs that also increased on July 1. Departure taxes increased from 1,000 yen to 3,000 yen ($18), while visa fees jumped from 3,000 yen to 15,000 ($92) per person, in their first increase since 1978. — CNBC's Matthew Tan and Lim Hui Jie contributed to this report.