Contract or SIM-only? The real cost of a new phone

AI SLAA SL Accessible

Research question

For a particular phone, is a 24-month contract cheaper than buying the phone outright (or with a loan) plus a SIM-only plan, once resale value and interest are included?

Adapt it: change the place, the data or the comparison until the question is yours.

Why it makes a good exploration

Phone contracts hide the phone's price inside the monthly bill. Separating the two with financial mathematics gives a clear answer about a purchase almost every student makes.

The mathematics you'll need

Total cost and implied interest rate (TVM)
Resale value modelled with depreciation
Break-even analysis
Linear and piecewise cost functions

Course labels show where a technique sits; using maths from outside your course is fine if you explain it clearly and say it is new to you.

Where the data comes from

Collect current prices for one phone model from network and retailer websites; resale prices of older models from resale sites.

Desmos graphing calculator — Free graphing and regression (y₁ ~ ax₁ + b) — fit models to your data and show residuals.

Cite every source in a footnote where you use it and in your bibliography. Check the licence of any dataset you download.

A possible outline

Define comparable options.
Compute total cost for each.
Find the implied interest rate of the contract.
Include resale value and different usage needs.
Reflect on price rises during contracts and flexibility.

Pitfalls that cost marks

Comparing different data allowances.
Ignoring mid-contract price rises.
Undated prices.

Showing personal engagement

Use your own phone and plan.
Compare with what your family pays.
Advise a friend with different usage.

See Criterion C: personal engagement for what examiners look for.

Taking it further

Build a general rule: for which phone prices and SIM prices is a contract ever cheaper?

Turn this idea into your IA

Plan this IAOpens the planner with this question, the maths and data sources filled in. Desmos workspacePlot your data, fit models and keep your graphs with your plan. AI feedback on a draftCriterion-by-criterion feedback with evidence from your own text. Coaching, not rewriting. Examiner reviewPete, a practising IA examiner, reads your draft and talks it through with you (€100).