Compared to most Android phones, Apple iPhones keep their value quite well, meaning you are usually able to sell your iPhone for a decent amount when the time comes for you to upgrade. But a firm that specialises in selling secondhand tech is warning that resale value could drop by up to as much as 30 percent after the iPhone 17 launches.

Sam Wilson, director at Gadget GoGo, warns that if you own an iPhone and are thinking of selling it to help fund your next smartphone purchase, you only have 30 days to do so before you can expect a drop in your handset’s current resale value.

"The iPhone resale market stays the same year after year, yet most people still wait until after the new models are announced to sell their old phones," Wilson said. "By then, it's too late, and the market becomes saturated with old models and values drop."

He said the mere announcement of a new iPhone will trigger a similar price drop on existing phones that has been seen in previous years, where iPhones are aged by the introduction of a new model.

"Pro and Pro Max versions can lose £150-300 in value within the first month after a new launch,” Wilson said. “That's a lot of money they could have pocketed by acting just a few weeks earlier."

So, if you have an iPhone 16 Pro or 16 Pro Max and are considering selling it to fund your iPhone 17 purchase, now could be the time.

Wilson even says that older phones such as the iPhone 13 from 2021 or iPhone 14 from 2022 would sell for more now rather than in a month’s time.

"Even if you're using an iPhone that's a few years old, you'll still see a big drop in value after the new announcement."

According to rumours, Apple is set to announce the iPhone 17 on September 9, 2025, which is in line with the usual Tuesday date. If the tech giant acts as it has in previous years, that could mean the iPhone 17 line up will be available for pre-order on Friday September 12, which gives you 30 days from today to sell up by September 11.

The iPhone 17 is rumoured to be joined by the iPhone 17 Pro and 17 Pro Max, as well as a special new ultra-thin model, potentially to be named the iPhone 17 Air.

These handsets could go on general sale on Friday September 19, by which time Wilson reckons your current iPhone won’t sell for as much as the secondhand market currently deems it is worth.

"iPhones generally retain their value better than other brands, which makes the timing of selling even more important. You're starting from a higher resale value, so the actual amount you lose by waiting can be huge," he said.

"Start the selling process now, even if you plan to upgrade in September. A lot of buyback services allow you to lock in a price today but keep using your phone for a few more weeks."

People are holding onto their phones for longer as they see little reason to upgrade year over year. If that’s you, and your iPhone is a few years old, it seems the advice is to sell as soon as possible if you want to recoup as much of the initial cost as possible.

You could of course put this money towards a refurbished or secondhand phone rather than stumping up hundreds for the latest iPhone 17 when it hits stores.