Renewing your mobile or broadband contract is an opportunity to reduce a household bill, but the cheapest headline price is not always the best value. This guide gives you a repeatable way to compare SIM-only deals and broadband offers using total contract cost, allowance, speed, coverage, fees, future price changes and switching incentives.
Overview
When a contract ends, start by separating the service you need from the deal you currently have. For mobile, that usually means deciding how much data, calling and texting capacity is appropriate. For broadband, focus on the connection speed and reliability needed by your household rather than automatically choosing the fastest package.
A useful comparison should answer four questions:
- What will the service cost over the full initial term?
- Does the allowance or speed match your actual use?
- Are there one-off costs, equipment charges or delivery fees?
- What could the price become after an introductory period or during the contract?
Do not compare a SIM-only plan with a handset-inclusive mobile contract as though they are identical. A handset plan may include the cost of the phone, while a SIM-only deal covers connectivity only. Likewise, a broadband offer may include a router, installation or a short-term incentive that changes the first-year cost.
For a broader mobile comparison, see our guide to comparing UK SIM-only deals. It can be used alongside the calculation method below whenever your usage or available offers change.
How to estimate the real cost
The simplest comparison is to calculate the total cost for the minimum period you expect to keep the service. Use this formula:
Total cost = monthly payments + one-off charges - guaranteed discounts
For a longer view, calculate the effective monthly cost:
Effective monthly cost = total cost divided by the number of months assessed
Only include a discount if the terms make it clear that you qualify and how long it lasts. Treat cashback, gift cards and loyalty rewards separately unless you would genuinely use them. A reward that requires extra spending should not be counted as an automatic reduction in the bill.
For mobile, add the monthly SIM price, any activation or delivery fee, and any expected cost for extra data. If you are replacing a handset, calculate the phone cost separately so you can compare buying it outright with paying through a contract.
For broadband, include the monthly subscription, setup or installation charges, equipment costs, and any required add-ons. If the advertised price applies only for an opening period, calculate the cost for that period and the remaining months separately. This makes it easier to compare a low introductory price with a steadier offer.
A spreadsheet is useful, but a simple note will work. Record the provider, plan name, contract length, monthly price, fees, allowance or speed, discount end date and expected price after the offer. Keeping the same headings each time makes future comparisons faster.
Inputs and assumptions
Use the following checklist before judging cheap broadband deals in the UK or cheap SIM-only deals.
Mobile inputs
- Data: Check recent usage in your phone settings or account rather than guessing. Allow for travel, hotspot use and video streaming if these are regular activities.
- Coverage: Check the network coverage where you live, work and travel. A lower price is poor value if the service is unreliable in the places you need it.
- Contract length: Compare like with like where possible. A longer term may lower the monthly payment but can reduce flexibility.
- Handset: If you need a new phone, include its total cost, not just the monthly instalment.
- Roaming and extras: Check whether travel use, premium numbers, international calls or additional data are charged separately.
Broadband inputs
- Required speed: Consider the number of people online, video calls, streaming, gaming and large downloads.
- Availability: Enter your exact address into each provider’s checker. Packages and technologies can vary by location.
- Contract term: Note the minimum term and whether leaving early could create a charge.
- Installation and equipment: Record setup, delivery, router and optional Wi-Fi equipment costs.
- Price changes: Write down any stated increase, review date or end of introductory pricing. If the future amount is unclear, mark it as unknown rather than presenting an estimate as certain.
Coverage and availability should be treated as personal inputs, not general assumptions. Before switching broadband provider, check the service at your address and confirm whether the proposed start date works with your existing contract.
Worked examples
The figures below are illustrations only. Replace them with the prices and terms shown in the offers you are considering.
Example 1: comparing two SIM-only plans
Suppose Plan A costs £12 per month for 12 months with no fee. Its total is £144, or £12 per month. Plan B costs £9 per month for the first six months, then £15 per month for the next six months, with a £5 delivery charge. Its total is (£9 × 6) + (£15 × 6) + £5 = £149. The effective monthly cost is £149 ÷ 12, or approximately £12.42.
Plan B is not cheaper over the year despite its lower opening price. It may still be preferable if it offers more data or better coverage, but those benefits should be recorded alongside the cost rather than assumed.
Example 2: comparing broadband offers
Imagine Offer A costs £28 per month for 18 months and has a £10 setup fee. The total is (£28 × 18) + £10 = £514, giving an effective monthly cost of approximately £28.56.
Offer B costs £24 per month for the first six months and £31 per month for the following 12 months, with no setup fee. Its total is (£24 × 6) + (£31 × 12) = £516, or approximately £28.67 per month across the term.
The difference is small, so speed, availability, equipment and the provider’s service terms may matter more than the headline saving. This is why a broadband comparison should consider the complete package rather than ranking offers by the first monthly figure alone.
When to recalculate
Revisit your comparison whenever your contract approaches its end, but also recalculate when the underlying inputs change. Useful triggers include a change in monthly price, a new data requirement, a move to a different address, a household member starting regular home working, or a new device that increases streaming or hotspot use.
Recheck the figures if an introductory discount ends, an included allowance changes, a provider adds a fee, or a switching incentive expires. Prices and availability can change, so an old comparison should not be treated as a current ranking.
Start the renewal process by finding your end date and downloading recent bills or usage information. Then:
- List your current monthly cost, allowance, speed and remaining contract term.
- Calculate your current annualised cost using the latest confirmed price.
- Compare at least a few suitable alternatives using total cost, not just the opening price.
- Check coverage or address availability before relying on an advertised offer.
- Ask your current provider whether it can improve the terms, but compare any retention offer on exactly the same basis.
- Save the final price, contract length, fees and review date in your calendar or household budget.
For savings across other household spending, our guides to stacking UK discounts and finding cheap laptop deals offer similar ways to compare the real value of an offer. Return to this calculation whenever your bill, usage or available deals change.
