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Estimate reach and frequency from a GRP budget

This job turns a planned GRP total into an expected 1+ reach percentage and average frequency against the target universe, using a reach curve to show diminishing returns. It feeds the decision on whether the current weight meets the campaign's reach objective or needs more GRPs added.

What you need first

  • GRP budget for the flight, from the media plan or client budget brief
  • Target audience definition and universe size, from the brief's specified demo (e.g. adults 25-54, population or panel data for the market)
  • Reach curve for the target group and channel mix, from the buying agency's syndicated research or the channel's own curve (Sainsbury, Naples, or empirical panel data)
  • Flight length and spot distribution pattern, from the media plan (continuous vs pulsed)
  • Comparable past campaign results at similar GRP weight, from the agency's plan archive

The procedure

  1. Confirm the target universe size and audience definition stated in the brief
  2. Read the 1+ reach percentage off the applicable reach curve at the planned GRP level
  3. Multiply reach percentage by universe to get the number of people reached
  4. Divide GRP by reach percentage to get average frequency
  5. Adjust the reach figure down if the flight is pulsed rather than continuous, since the same GRPs spread in bursts reach fewer people
  6. Compare the resulting reach against a comparable past campaign at similar weight in the same market
  7. Record the curve source and assumptions alongside the reach and frequency figures before handoff

Worked through with numbers

Universe: 3,000,000 adults 25-54 in the market. Planned budget: 800 GRPs over a 4-week continuous flight. The channel's reach curve for this demo shows 1+ reach of 62% at 800 GRPs. Reached population = 3,000,000 x 0.62 = 1,860,000 people. Average frequency = 800 / 62 = 12.9 opportunities to see per reached person. Read this as: the budget covers 62% of the target universe, and each person it reaches sees the campaign about 13 times on average, which is heavy frequency for a single flight and worth flagging if the objective was breadth rather than depth.

Where it goes wrong

  • Reach is corrected for the curve's diminishing returns, not read as a straight-line function of GRPs, since doubling GRPs never doubles reach once the curve starts flattening
  • The reach curve used matches the actual channel mix and market, not a national curve applied to a local or regional buy
  • When combining channels, net reach across TV and digital is calculated with a duplication adjustment, not by adding each channel's reach percentage
  • Average frequency is reported as a mean, not mistaken for the frequency every reached person gets, since the underlying distribution is skewed toward light and heavy viewers

How to know it is right

Confirm that reach multiplied by average frequency reproduces the input GRP total exactly, and that the reach figure sits below the curve's known ceiling for that market and daypart rather than approaching 100%.

Terms used

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