Estimating reach with clearly stated assumptions

A reach estimate should say who might be reached, what event counts as reach and which assumptions connect the audience to the plan. Show a range when inputs are uncertain, and label it a planning estimate until delivery is reported.

Define the audience and reach event

Specify the eligible people, geography and campaign period, then define “reached” — for example, a person served an ad at least once under a specified plan.

Keep the unit as people only if the method estimates people. Devices, accounts and impressions need their own labels.

A population source can supply context, but it is not automatically a campaign denominator.

ABS QuickStats describes residents at a Census date; its person figures use usual residence. A Census population figure alone may not identify today's eligible buyers or people addressable by a particular campaign.

Treat any ad-reach estimate as guidance, not as a forecast for a booked campaign.

Show the calculation and its assumptions

Consider a purely hypothetical area with 10,000 people under a stated audience definition.

Assume 50–70% are eligible for an offer. Of those eligible, assume 30–60% would be served at least one ad during the planned period.

Applying the low assumptions together and the high assumptions together gives:

These inputs are invented to show the method. They are neither Australian market findings nor a supplier forecast.

The delivery percentage is conditional on eligibility, and both percentages must have a credible basis before the range can be treated as a forecast. Otherwise, the calculation is a sensitivity exercise. The two scenarios are not guaranteed bounds on actual delivery.

Keep an assumption register beside the calculation: the source and date of the audience base, the basis for eligibility, the placement and settings behind expected delivery, who supplied each input, and when it should be reviewed. Note any unknown coverage or overlap.

Check the supplier's measure

Ask whether a supplier's reach figure covers its whole property, advertising inventory or the precise proposed plan. Request the target definition, locations, formats, dates, budget, frequency setting and any modelling or exclusions. Compare the forecast with what will actually be booked.

For any Reach Planner estimate, request the target definition and inputs, and present it as a planning estimate rather than a guaranteed outcome.

Check what the reported reach measure counts and which geography and audience definition it uses; do not label it a count of local residents unless the method supports that.

If a supplier does not provide a reach percentage, ask what prevents a usable estimate. Do not fill the gap with an unrelated population figure.

Present each plan's estimate with its assumptions. Do not add separate suppliers' unique-reach figures into a combined unique audience without evidence about overlap.

Use the range

Ask whether the low scenario would still offer a worthwhile chance to contact eligible people. If the decision changes across scenarios, identify the assumption worth checking before booking.

After launch, compare the actual settings and available delivery report with those assumed. Investigate differences without treating either the model or the report as a complete count of eligible buyers.