Podcast advertising is bought on a different basis from most digital media, and the difference explains why rates hold up even where measurement is weak. The unit of sale is a download, not an impression.
The unit is a thousand downloads
Advertisers pay an agreed amount for every thousand downloads an episode receives, which means the price of a campaign is set by audience size rather than by any observed response.
Because the count accrues over time, a show sells against a forecast of what an episode will reach within a set window after publication, commonly a month.
If the episode undershoots that forecast, the shortfall is usually made up with additional inventory rather than refunded, which is why campaigns often run longer than originally scheduled.
A download is not a listen
A download is registered when an application requests the audio file, which happens automatically for subscribers whether or not anyone eventually presses play.
Measurement standards exist to strip out obvious duplicates and partial requests, but the figure remains an upper bound on attention rather than a measure of it.
Advertisers compensate with discount codes and dedicated landing pages, which capture only the fraction of listeners who act immediately, so both numbers mislead in opposite directions.
Position within the episode changes the rate
Spots are sold by slot. A read before the content begins, one in the middle and one at the close are priced quite differently from each other.
The mid-roll typically commands the highest rate, because a listener who has stayed that far into an episode is unlikely to abandon it over an advertisement.
Pre-roll reaches the largest number of people but sits where skipping is easiest, and the closing slot reaches the fewest, which is reflected in what each costs.
Host-read and produced spots are separate products
A host reading copy in their own words is sold at a premium, since the endorsement borrows the trust the audience has already extended to that voice.
A pre-produced advertisement supplied by the brand costs less and can be inserted automatically, which makes it far easier to schedule across many shows at once.
Dynamic insertion allows either type to be swapped out later, which turns the archive into inventory that can be resold rather than a fixed recording.
The back catalogue sells at a discount
Older episodes continue to be downloaded for years, and those downloads are packaged and sold separately from the release-window inventory at a materially lower rate.
The audience arriving late is smaller per episode but spread across the whole archive, which makes it valuable to advertisers with long campaigns and no fixed date.
That long tail is also why shows resist deleting old episodes. Each one remains a small, permanent piece of sellable space.