Percent Blocked Calls
Definition
Percent Blocked Calls
Percent blocked calls is the share of inbound calls that fail to reach an agent or queue because of trunk, network, or capacity limits. A healthy rate stays under 2%, and anything higher signals under-provisioned lines or thin staffing during peaks. The metric flags infrastructure gaps that queue-time KPIs miss entirely.
Every blocked call is a customer who never spoke to anyone. They hear a busy tone, a fast-busy, or a network error before an IVR can even pick up. That silent friction erodes revenue and CSAT in ways queue-based metrics never capture.
Trunk-side blocking happens when every voice channel on your PBX or SIP trunk is in use. Carrier-side blocking happens upstream at the telco. Both roll up into the same percent-blocked-calls figure your workforce management team reports each morning.
Key takeaways
- Formula: blocked calls divided by total inbound attempts, times 100.
- Healthy benchmark sits under 2%; anything over 5% is a hard alert.
- Peak-hour spikes usually trace to trunk provisioning, not agent shortage.
- Fixing the rate takes SIP capacity planning plus accurate intraday forecasting.
- The KPI complements — but does not replace — call abandonment and average speed of answer.
How it works
Percent blocked calls counts every attempted inbound call that the phone platform rejects before it enters the queue. The formula is simple:
Percent blocked calls = (Blocked calls / Total inbound call attempts) × 100
A call-centre platform logs a block whenever an incoming call hits a maxed-out trunk group, a full-queue overflow rule, or a carrier-imposed congestion signal. That reject fires before any agent or IVR menu picks up, so the caller never registers on downstream KPIs like ASA or handle time.
Three levers drive the number up:
- Under-provisioned SIP trunks or PSTN lines during known peak windows.
- Poor intraday forecasting that under-staffs demand spikes.
- Overflow rules configured to block calls rather than route to backup queues.
| Percent blocked calls | Status | Typical cause |
|---|---|---|
| Under 1% | Excellent | Trunks and staffing well-matched |
| 1–2% | Healthy | Normal peak-hour fluctuation |
| 2–5% | Watch | Forecasting or trunk gap |
| Over 5% | Alert | Under-provisioned capacity or carrier failure |
Contact-centre research firm ContactBabel places the median blocked-call rate for UK operations at roughly 1.4% in its 2024 Decision-Maker’s Guide, with financial-services and utilities queues running higher during outage events.
Examples
Concentrix, Manila (2024). During a Q4 retail-season surge, the Ortigas campus reported blocked-call rates edging above 3% on a US electronics account. Adding 30% SIP-trunk headroom over two weeks pulled the metric back under 1.5%.
Teleperformance, Lisbon (2023). A voice-of-customer audit flagged that 4.2% of daytime calls to a European bank’s premium line were blocked at the carrier level. Adding a redundant SIP provider dropped the figure to under 0.8% inside a quarter.
TTEC, Bogotá (2025). After migrating an insurance client onto cloud voice, TTEC’s Colombia contact centre held blocked calls at 0.6% across a 12-month window, a benchmark the client cited when renewing.
Foundever’s UK healthtech account (2024) ran percent blocked calls at 2.8% until a joint forecasting review with the client rebuilt the intraday staffing plan and cut it to 1.1%.
Related terms
- Call abandonment: calls that enter the queue then hang up before an agent answers — the downstream cousin of blocked calls.
- Average handle time: the mean length of an agent-caller interaction, including hold and wrap.
- Service level agreement: the contract that usually caps blocked-call thresholds explicitly.
- Interactive voice response: the self-service menu callers hit only AFTER the trunk admits them.
- Workforce management: the discipline that forecasts and schedules the capacity blocked calls expose.
- Occupancy rate: the flip-side metric measuring how saturated agents already are.
- First call resolution: the quality KPI that suffers most when repeat callers pile onto already-blocked lines.
FAQ
What causes percent blocked calls to spike?
Under-provisioned trunks, unexpected volume surges, and carrier congestion top the list. Poor intraday forecasting is the most common controllable cause, and most spikes trace back to a staffing model that missed a demand peak by 20% or more.
What is a good percent blocked calls benchmark?
Under 2% is healthy for most inbound queues. Financial services and healthcare targets sit tighter, often under 1%, because a blocked call may be safety-critical. Over 5% is a hard alert flagged in most SLAs.
How is percent blocked calls different from call abandonment?
A blocked call never enters the queue: the caller hears a busy tone or network error. An abandoned call enters the queue and then hangs up before an agent answers. Blocked calls point to infrastructure gaps; abandoned calls point to wait-time frustration.
Does IVR affect percent blocked calls?
Only indirectly. IVR sits AFTER the trunk, so a call must already be admitted before the menu plays. But IVR misrouting can push callers back into the main queue, saturating trunks and lifting blocking downstream.
Who owns percent blocked calls in a contact centre?
The workforce-management team and the telecoms lead usually share it. WFM handles forecasting and staffing; telecoms manages trunk capacity and carrier redundancy. Ops directors review it weekly against the SLA.
How often should you review the metric?
Daily at minimum, with intraday sampling during known peaks. Deloitte’s 2024 Global Contact Center Survey found that centres reviewing capacity KPIs every four hours cut blocked-call rates roughly 40% faster than those reviewing weekly.
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