Reading a data plan like an actuary: the five numbers that decide the price you actually pay

Two identical plans can cost the same person different money in the same month, because a data plan is not one number - it is five, and the bill you feel is the maths between them. This page does not quote prices or provider tables (both change on a schedule nobody outside the companies knows in advance); it teaches the reading, which survives every price change, and the one-line arithmetic that turns 'unlimited' into a sentence you can check against your own meter.

The five numbers, each with the question it hides

• Volume and validity: the gigabytes are a rate over a window, so the honest question is consumption speed, not size - 10 GB over a week is a heavier throttle than 10 GB over a month even though the listing shows the same figure. The desk's method: your real weekly use comes from the phone's own data meter across a normal week (settings, Battery and usage / Data - the phone keeps the ledger), not from the provider's app, which reports after rounding.
• Rollover, or its absence: unused data dying at expiry is a discount you paid but never got; a genuine rollover changes how aggressively to buy the top-up tier - the clause lives in the plan's own terms page, and the difference between 'rolls over' and 'on active bundle' is a whole tier's value.
• The night window: where providers sell off-peak data at fractions of the price, the correct move is not moralising about speed - it is scheduling: app updates, backups, the film download for tomorrow, all land the phone can do unattended between midnight and dawn, and the window's hours are printed on the offer's page, so verify them rather than trusting the folklore. The honest caveat: night data that cannot tether turns the bargain's maths against the hotspot household.
• Tethering clauses: some plans meter hotspot use separately or forbid it - the clause is in the terms, the setting is in the phone (limit hotspot to the laptop's own downloads), and the household that runs a router off a phone lives or dies by this single paragraph.
• Throttling and 'fair use': the fair-use ceiling on an 'unlimited' is the plan's real volume - once the phone's meter meets the number in the terms PDF, 'unlimited' becomes the reduced speed the same page names. The one-line exposure: divide the cost by the fair-use volume, not the headline infinity; that figure, compared with the honest capped bundle, is the whole purchase decision.

The calculation, and why it beats the ranking list

Per-gigabyte price after your real behaviour: cost divided by the data you can actually consume within validity, minus the uses the plan excludes. The reason no review article can do it for you is that the numerator moves quarterly and the denominator is your life: the family that watches streamed television on tethered tablets and the student who downloads coursework at the campus window have different answers to the same listing. The habit that keeps the maths current: before each renewal, the phone's week-of-data meter against the plan's five numbers - two minutes, and the 'is there a better plan' question stops being answered by whoever shouts loudest in the adverts.

The top-up trap, stated once

Buying small because small feels safe is the plan's own subscription to your impatience - repeated micro-purchases almost always sum above the tier that would have covered the month, and the provider's app will happily show every one as 'value'. The desk's rule: the phone meter sets the tier, the tier gets bought once, and the small top-up exists for the week that surprises, not the budget.

Check before you commit

The plan's own terms page for the five numbers (validity, rollover wording, night hours, tethering, fair-use volume and post-cap speed) - then the phone's data meter for the denominator. Every figure on this page lives in one of those two places, which is exactly the point: the reading outlives the listing, and the listing is where the argument starts.