Phone and internet: getting the work percentage right

Phone and internet claims are common, small, and frequently unsupported. The amount is rarely the problem; the percentage is.

flowchart TD
  claim[Phone or internet claim] --> wfh{Using the WFH fixed rate?}
  wfh -->|Yes| inside[Already inside the rate - do not claim again]
  wfh -->|No| diary[Keep a four-week representative diary]
  diary --> apply[Apply that percentage to the year]

First, check you aren't double-dipping

If you claim working-from-home running costs using the fixed rate (70c per hour for 2025–26), then internet, data, mobile, and home phone usage are already inside that rate. You cannot claim them again separately. That single rule invalidates a lot of otherwise-sensible claims.

Separate phone and internet claims make sense when you:

• use the actual cost method for working from home, or
• use your phone or data for work in ways unrelated to working from home — client calls in the field, work hotspot on the road, on-call duties

The four-week representative diary

The standard way to establish a work-use percentage is to keep a diary over a continuous four-week period that is representative of your usual pattern, then apply that percentage to the year.

For a phone with an itemised bill, count over the four weeks:

• work calls made and received, as a share of total calls
• work data used, as a share of total data
• work texts, as a share of total texts

For a bundled plan you can't itemise, a reasonable basis is time spent on work use versus total use — but write down how you measured it.

A worked example. Over four weeks: 60 of 200 calls were work, and 6 GB of 20 GB was work data. Weighting by how you actually use the service, you land on roughly 30% work use. On a $65 monthly plan, that's about $234 for the year.

Internet is usually the harder one

Internet is shared with a household, and household use is private. Bases people use, in rough order of defensibility:

Basis	Notes
Data volume, work vs total	Strongest if your router or ISP reports it
Time connected for work vs total household time	Reasonable, needs a diary
Number of household users	Weak on its own; a fallback at best

Whatever you use, the requirement is the same: keep the workings, not just the answer.

Things that quietly break a claim

• Employer-provided or reimbursed services. If your employer pays the bill or reimburses you, it isn't your expense.
• A plan in someone else's name. You must have incurred the cost.
• Round numbers with no basis. "50%" appears in an enormous number of returns. It's fine when you can show why, and indefensible when you can't.
• Handset cost mixed into the plan. A phone bundled into a plan is partly a depreciating asset and partly a service; they're claimed differently.

Keep it light

You only need one four-week diary, refreshed when your work pattern genuinely changes. Store the percentage and the sentence that justifies it next to the expense itself, and every future year's claim inherits a documented basis rather than a fresh guess.

That's the whole discipline: a small percentage, honestly derived, written down once.