What is the roundtrip train fare from Gatwick to London and back?

one way is £11, return is £21.50, and day return (round trip on the same day) is £11.70

Assuming you're not going from Gatwick to London and back on the same day, your cheapest option would be to buy an open return ticket on South Central trains. Your open return (roundtrip) ticket would cost 16.40 GBP, the route is the same as the Gatwick Express, and the trip will take only five to ten minutes longer. Visit www.qjump.co.uk for the timetables and prices.

TimS is correct - my answers were for the Gatwick Express to Victoria. Thameslink and South Central would be cheaper.

Hit post before I was done -- your title mentioned the Gatwick Express so those were the fares I quoted . . . . . .

I've heard there's not as much luggage space on those other trains as there is on the Gatwick Express.

There are also some 4 for 2 deals on the Gatwick Express.

I think all of the trains have some sort of deal that you can get with an off-peak TravelCard too - but I don't know the details.

I'm fairly sure my son's ISIC card helped him get a discount on the Gatwick Express.

Thanks for the replies. This was for round trip on the same day - killing time during a layover. Any additional advise?