The true cost of a phone contract is the total of every compulsory payment, not the number printed largest in the advert. A fair comparison also uses the same handset, storage, term and airtime allowance.
The basic calculation
Start with:
Upfront payment + all scheduled monthly payments + compulsory one-off charges + any final payment.
Then keep optional or usage-dependent spending separate, such as insurance, roaming, premium services and out-of-bundle use. This prevents an optional choice from being mistaken for part of the contract price while still showing what ownership may really cost you.
Illustrative example
Illustrative figures only — not a current market offer.
| Cost | Calculation | Amount |
|---|---|---|
| Upfront payment | One payment | £49 |
| Months 1–9 | 9 × £31 | £279 |
| Months 10–21 after a stated rise | 12 × £33 | £396 |
| Months 22–24 after a second stated rise | 3 × £35 | £105 |
| Total contractual payments | £49 + £279 + £396 + £105 | £829 |
The example shows why multiplying the opening monthly price by 24 would be wrong. Use the exact dates and amounts in the contract summary.
Separate the handset and airtime where possible
If the documents state the device and airtime prices separately, record them separately. If they do not, create a comparison benchmark:
- Find the cash price of the exact handset from a suitable seller.
- Find the cost of a SIM-only plan that covers your real usage over the same period.
- Add those two figures.
- Compare the result with the full handset-inclusive commitment.
The difference is not automatically “interest”. It may reflect financing, a network subsidy, a retailer discount, a larger allowance or a different service. The calculation tells you where to investigate; it does not by itself explain the difference.
Costs that belong in the contractual total
- upfront payment;
- monthly airtime and device payments;
- scheduled rises already written into the agreement;
- mandatory delivery, activation or connection fees;
- a compulsory final or purchase payment;
- an unavoidable accessory or service bundled into the offer.
Costs to show separately
- insurance you can decline;
- international or roaming use;
- premium-rate services;
- extra data or calls beyond the allowance;
- late-payment charges;
- early-exit or early-settlement amounts;
- accessories, repairs and eventual resale value.
These costs may be avoidable, uncertain or personal to the user. They still matter, but mixing them into one headline total can make comparisons misleading.
Do not subtract cashback until you understand it
Automatic cashback paid shortly after purchase is different from a redemption scheme that requires several correctly timed claims. Record conditional cashback separately and count it only if you can meet every term. A deal should remain affordable even if a claim is missed or rejected.
Compare equal periods
A 24-month deal and a 36-month deal should not be compared only by monthly price. Compare:
- the full contractual total;
- the average monthly cost over the whole term;
- the point at which you own the device;
- the expected useful life remaining when payments end;
- the cost of leaving early.
Use three totals, not one
A single number can conceal uncertainty. Record:
| Total | Includes | Purpose |
|---|---|---|
| Contractual minimum | Every compulsory payment in the agreement | Shows the amount you are committed to pay if usage stays within the plan |
| Likely ownership cost | Contractual minimum plus realistic extras, accessories and repairs | Supports household budgeting |
| Exit scenario | Payments made to date plus written termination and settlement figures | Shows the risk if circumstances change |
Handle discounts carefully
A discount may apply for the full minimum term, for a fixed number of months or only while another condition remains satisfied. Calculate each phase. If the normal price begins before the minimum term ends, include it.
Do not treat a trade-in estimate as a contract discount until the old phone has been assessed and the final value confirmed. Keep trade-in value on a separate line so a later reduction does not make the new contract unexpectedly unaffordable.
Do not subtract uncertain resale value
Your new phone may retain value at the end, but resale depends on condition, battery, support life and the market at that time. Use residual value only as a separate scenario, not as money guaranteed to reduce today’s contractual commitment.
Check split plans
Where airtime and the device are billed separately, calculate each agreement independently and then combine them. This exposes different end dates and prevents a device balance from disappearing from the comparison simply because the airtime minimum term is shorter.
Calculate your contractual minimum
Copy the figures from the contract summary into your own calculation before applying. Then use How to Compare Phone Deals Correctly to compare alternative routes and Hidden Costs in Phone Contracts to inspect non-headline charges.
Check ownership, settlement and early exit separately
The contractual total does not by itself tell you when the handset becomes yours or what it costs to leave. Read the airtime, device and finance documents separately. Record the ownership point, the current settlement method and whether an early upgrade requires the phone to be returned.
| Question | Why it changes the comparison |
|---|---|
| When do you own the phone? | A return-based upgrade is not the same as buying an asset you can later sell. |
| How is early settlement calculated? | The remaining device balance can continue after the airtime minimum term ends. |
| What happens if you leave the airtime plan? | A device agreement, insurance or promotional condition may continue separately. |
| Is an upgrade optional or conditional? | A headline upgrade date can depend on returning the existing device in an accepted condition. |
Before signing, ask for the contractual minimum, the ownership position and a written example of the exit cost at a realistic point in the term. A deal that is affordable only while every discount and upgrade assumption works perfectly is not a resilient contract.
Sources and fact-checking
Facts checked: 25 July 2026. All figures above are illustrative.
