If you don’t remember exactly when your phone contract first started, chances are you won’t know when it ends. Knowing how long you’ve got left on your contract is useful: it enables you to know when to start thinking of upgrading and when you can renew or start researching other providers. (Our article on the best phone networks might help).

It's also really important to know when your contract ends in order to ensure that you don't keep getting charged for a phone that you've actually finished paying for. Most contracts combine a payment for the SIM and a payment for the phone, so once you've finished paying off the phone (at the end of your contract) you should be able to reduce the cost of your contract significantly if you decide not to upgrade.

Then you can decide to start a new contract and get a new phone, starting the whole process off again - or simply switch to a SIM-only deal, where you pay a much reduced monthly fee just for your calls/texts/data but keep your current phone. With SIM-only deals starting at £4/month this could save you £20-£40 a month!

Check out the best SIM-only deals in our roundup, which is updated to find the best deals each day, and you can click here to skip to the bottom of this article for a customisable SIM-only price comparison tool.

According to Citizens Advice, more than six million customers are being charged for their mobile phones for longer than they should be. Once you've paid off the phone you really should change your contract. Otherwise you are paying for your phone again!

Here is how to tell how long you’ve got left on your phone contract.

If you’re an EE customer

Login to ‘My EE’ and check your upgrade status. This will tell you the exact date when you’re next eligible for an upgrade. For EE customers, upgrades become available exactly 45 days prior to the contract end. So simply add 45 days to the date shown and you’ll get your contract’s end date. You can also text 'UP' to 150 to find out your upgrade date and follow the same process.

If you’re a Vodafone customer

There are three ways to check how long you have left on your contract for Vodafone customers. You can login to ‘My Vodafone’ and go to ‘Upgrade or change plan’. Your contract’s end date will appear.

You can also find out the end date through the Vodafone app. Go to ‘My product and services’ and then click ‘My plan’. It will tell you when your contract ends.

The final way is to call 191 and ask customer service, or to check your bill or welcome email on which your contract’s start date will appear. You can figure out how long you’ve got left by adding the contract’s length to the start date.

If you’re an O2 customer

O2 customers simply have to login to ‘My O2’  and go to ‘My tariff summary’ to find the contract’s end date. Alternatively, they can also call 202, which is free of charge from an O2 mobile.

If you’re a Three customer

Login to ‘My3’. Go to ’Upgrade and offers’ and select ‘Check if you can upgrade’. Your contract's end date will appear under ‘Your minimum term finished on’. It will also be available on the letter or email you received when you first joined Three. If you can’t find it, call 333 or 0333 300 3333 and ask customer service, free for all Three customers.

If you’re a Tesco customer

If you’re a Tesco customer, login to your ‘Pay Monthly’ account to view your end date. You can also call 4422, which is free for all Tesco clients.

When you're ready to upgrade, check out our guide to the best phones of 2017.