Analysis by NetVoucherCodes found that Ryanair levied the most for extras such as seat selection, baggage check-in and insurance. It found that 89% of all airlines charged for at least one extra, with the figure rising to 97% among European carriers.

The rise in charging for flight add-ons has resulted in almost nine out of 10 airlines charging for at least one additional fee on top of the headline price for a flight, according to NetVoucherCodes.

Ruth Jaffe, 79, and her husband, Peter, 80, were charged £110 to check in with Ryanair after accidentally downloading their return boarding passes instead of those for their outgoing flight when they flew from Stansted Airport to Bergerac, France.

The charges they incurred prompted others to complain about Ryanair’s fees on social media.

The rise of paid-for add-ons

Extras fees on flights are a relatively new thing – Ryanair began the trend in 2006 by charging passengers a £2.50 fee for checked luggage, followed by £4 for “priority boarding” in 2007.

By 2011, other airlines joined in a bid to make their airfares look cheap while pushing costs into optional add-ons. Numerous airlines started charging for checked baggage, seat selection, quick boarding and different-sized hand luggage.

Seat allocation charges

NetVoucherCodes found that seat selection charges were the most prevalent hidden fee when it analysed airlines both in Europe and the US.

It found that some budget airlines offer free seat allocation during online check-in, but they often separate passengers to encourage pre-booking. Seat selection costs can increase depending on where on the plane you sit and if the seat has more legroom.

The cost of booking a particular seat on a plane can range from anything between £3 to £100, depending on the airline you’re flying with and the class of travel. For example, if you’re flying business class on British Airways, it can cost you up to £91 to pre-book a seat.

EasyJet seat allocation prices range from 99p (standard seat) to £12.99 (extra legroom). Ryanair prices start from £3 for a standard seat, from £7 for a front seat, and from £14 for an extra legroom seat.

Combined costs

NetVoucherCodes examined a series of similar routes for the world’s top airlines and calculated the costs of add-ons such as carry-on baggage, 20kg checked bags, seat selection, fast tracking, insurance and onboard Wi-Fi.

Of the 35 European airlines it examined, Ryanair stood out with the largest percentage of hidden fees when compared with the base fare. NetVoucherCodes said the airline charged up to 344% of the fare price in extra fees. However, it conceded that Ryanair offered “incredibly low base fares” and so was giving passengers the benefit of a cheap flight where they can choose additional add-ons where necessary.

How to avoid airline extras

To avoid baggage fees, try fitting all your belongings into a carry-on bag. These tend to be free with budget airlines although you’ll be limited to a certain size bag.

Consider skipping seat selection during booking and try selecting seats for free during online check-in, within the 24-hour window. If you’re travelling in a group, book tickets together to increase the chances of being seated together without paying extra for seat selection.

If you need to check-in a bag, purchase the check-in online in advance, as it’s usually cheaper than paying at the counter.

Read your airline’s change fee policy before booking – you can often make changes within 24 hours of booking.

Research meal options before a long-haul flight to see what’s included as it might be cheaper to take your own snacks.