Cheap SIM Only Deals UK: How to Pay Less Every Month

A SIM only deal gives you a plan of data, minutes and texts without a new phone — and that's exactly why it's the cheapest way to stay connected in the UK. Rolling 30-day SIM only plans start from around £5/month, with no contract, no credit check and 5G included at no extra cost.

In this guide we'll show you what a good cheap SIM only deal looks like in 2026, how much data you actually need, and how to switch networks in minutes without losing your number. You can also compare today's best options on our SIM only deals comparison page.

What makes a SIM only deal cheap?

Three things decide whether a SIM only deal is genuinely cheap: the monthly price per GB, the contract length, and what's included. A £5 plan that charges you extra for calls you actually make is worse value than a £8 plan with everything unlimited.

• Price per GB: divide the monthly price by the data allowance. Rolling plans from Lebara and Giffgaff typically work out at £1-£2 per GB on mid-tier plans, and far less on unlimited.
• Contract length: 12-24 month contracts look cheaper per month but lock you in. Rolling 30-day plans let you switch the moment a better deal appears — and prices rarely reward loyalty.
• Included extras: unlimited UK calls and texts should be standard. EU roaming and international minutes are the tie-breakers — Lebara includes international minutes to 40+ countries, which is why it's popular with families calling abroad.

Cheap SIM only deals compared

Here's how the two networks we recommend stack up. Both are rolling 30-day plans with no credit check, so you can try one for a month and switch back if you're not happy.

Prices are indicative and change over time — always confirm current pricing on the network's site before ordering. For deeper comparisons see our PAYG vs monthly guide and our 5G SIM only deals page.

How much data do you actually need?

The fastest way to overpay is buying data you never use. Check your current network's app for your real monthly average before choosing a plan. As a rough guide:

• 2–5GB: messaging, email, maps and occasional browsing. Enough for most light users, especially if you're often on Wi-Fi.
• 10–20GB: daily social media, music streaming and some video. This is the sweet spot for most people.
• Unlimited: heavy video streaming, hotspotting a laptop, or replacing home broadband. At £20-£35/month it's still cheaper than a phone contract with less data.

How to switch to a cheap SIM only deal (without losing your number)

Switching takes one text message and about two working days:

• Step 1: text PAC to 65075 from your current number. You'll receive a switching code straight away.
• Step 2: order your free SIM (Giffgaff and Lebara both post SIMs free in 3-5 days) and activate it online.
• Step 3: give the PAC code to your new network. Your number transfers automatically, and your old contract ends.

If you'd rather start fresh with a new number, you can skip the PAC code entirely and just activate the SIM.

Mistakes that stop people getting the cheapest deal

• Buying a handset contract by default. If your phone works fine, a SIM only plan saves £20-£40/month versus paying off a new phone.
• Overestimating data. Most people use far less than they think. Start smaller — on a rolling plan you can upgrade mid-month if needed.
• Staying out of loyalty. Rolling plans make haggling pointless; if your price rises, just switch. Texting PAC to 65075 takes seconds.
• Ignoring roaming needs. If you travel, check our EU roaming SIM guide — not all networks still include it free.

Are cheap SIM only deals reliable?

Yes — because Lebara and Giffgaff run on Vodafone's and O2's full national networks respectively, not their own infrastructure. You get the same coverage and 4G/5G speeds as the parent network's direct customers. The difference is purely commercial: no handset subsidies, no shops, no long contracts — and those savings are passed on to you.

Final thoughts

Cheap SIM only deals are the single easiest way to cut a recurring monthly bill. Pick a rolling 30-day plan that matches your real data use, keep your number with a PAC code, and re-check the market every few months — with no contract, switching is always free.