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One of the sweetest travel deals of the summer quietly ends at midnight tonight. If you have an American Express card – and if the offer is showing in your account – you can earn £300 back when you spend £700 or more on United flights departing the UK. That’s a 43% rebate on any cash ticket priced at just £700.

The promotion applies to flights booked directly with United, and there’s no requirement to travel by a certain date. You just need to complete your booking before the offer deadline.

Why this matters

This is a rare chance to dramatically reduce the cost of long-haul flights. United’s network from Heathrow and Edinburgh includes key hubs like New York/Newark, Washington D.C., Chicago, Denver, Los Angeles, San Francisco and Houston. With a single round trip easily topping £700, the cashback effectively turns a £700 ticket into a £400 one.

Even if you were planning to pay with points, it’s worth running the numbers on this cash fare.

How to make the most of it

First, log in to your Amex account and check that the United Airlines £300 cashback offer is available, then save it to your card. Book your flights on United’s UK website united.com using the eligible Amex card.

Note that package holidays, car hire and award ticket fees do not qualify – you must buy a published airfare.

To earn Avios instead of MileagePlus miles, you can credit your flights to Aer Lingus AerClub and then combine points later. After your transaction posts, the £300 credit should appear on your statement within a few days.

Bottom line

It’s extremely rare to see a rebate worth almost half of your airfare. If you’ve been procrastinating about booking a trip to the US, today is the day to pull the trigger.