How to Choose a Buyer-Duration Threshold
60, 90, or 120 seconds? The number you pick changes your CPA, your conversion rate and your publisher pool. Here's how to think about it.
Every pay-per-call campaign has one setting that quietly controls everything else: the buyer-duration threshold — the number of seconds a call has to run before it becomes billable. Pick it right and your CPA drops. Pick it wrong and you either overpay or starve your pipeline.
What the number actually does
The threshold filters dropped calls out of your billable pool. A 60-second threshold means you pay for any connection that lasts a minute. A 120-second threshold means you only pay when the call has warmed up enough to be a real conversation.
Here's how the trade-offs sit in practice:
| Threshold | Billable rate | Downstream conv | Publisher supply | Best for |
|---|---|---|---|---|
| 60s | ~85% of connects | Baseline | Largest pool | New buyers, high-volume verticals |
| 90s | ~62% of connects | +14% vs 60s | Medium | Most enterprise buyers |
| 120s | ~41% of connects | +28% vs 60s | Smaller pool | Regulated / high-AOV sectors |
The maths that matters
The number to optimise is effective CPA — cost per converted customer, not cost per billable call.
Effective CPA = CPC ÷ (billable rate × downstream conv rate)
At £45 CPC:
- 60s at 85% billable × 8% conv → £662 CPA
- 90s at 62% billable × 12% conv → £605 CPA
- 120s at 41% billable × 16% conv → £686 CPA
For this profile 90s wins. But the sweet spot moves with your close rate. Sectors with strong AI-assisted qualification (Solar, HVAC) often clear better at 60s. Sectors with a slow discovery motion (Mortgages, Tax Debt) reward 120s.
The three signals to watch
- Median call duration on billable calls. If it's clustered near your threshold, tighten by 30s. If it's well above, loosen.
- Publisher supply availability. If your CPL desk keeps flagging under-cap days, you may be filtering supply too hard.
- First-week close rate. The stat that actually pays for the campaign.
The Connexis defaults
We recommend most enterprise buyers start at 90s. It's the median across our marketplace and gives you the widest publisher pool without the sub-conversion noise of a 60s bucket. Move up or down based on the three signals above after 30 days of live data.
Want to model your own numbers? Post a campaign → and the desk will walk you through it.