Short answer
Choose a power dialler if your team is small, the list is short or each conversation requires preparing the record: it dials only when an agent is free and never produces calls without an agent. A predictive dialler gives more conversations per hour, but if more people answer than forecast it produces abandoned or silent calls. Use it only with volume, several agents and daily abandonment reports per campaign.
Key verification: Ask the vendor for a daily report per campaign showing answered, agent-connected, abandoned and silent calls.
Sources and limitationsA power dialler, also called a progressive dialler, places a call only when an agent is free, so every person who answers finds someone on the line. A predictive dialler places more attempts than there are free agents because it expects that not everyone will answer; it gains talk time, but when more people answer than forecast it produces abandoned or silent calls. For small teams or short lists, a power dialler is usually enough; a predictive dialler only makes sense with volume, several agents and abandonment control that you can measure every day.
How each mode sets the pace
| Aspect | Power (progressive) | Predictive |
|---|---|---|
| When it dials | When an agent becomes free or finishes wrap-up | Before the agent becomes free, based on a forecast |
| Attempts per free agent | One | Several, adjusted by the system |
| Data it uses | Agent status | Contact rate, talk and wrap-up duration, agents logged in |
| What the person answering hears | The agent, who was already on the call | The agent, a message or, if the message is missing, silence |
| Main risk | Agent time spent listening to ringing | Contacts with no agent available |
Aircall's documentation describes its Power Dialer as a list dialled in order, with optional wrap-up time after each call before moving to the next number: using the Aircall Power Dialer, consulted on 22 October 2026. By contrast, Sinch's predictive configuration includes a maximum percentage of calls dropped because no agent is free, with a default value of 1.0, and warns that some countries restrict that value: Sinch predictive parameters, consulted on the same date.
Names do not guarantee behaviour
"Power", "progressive" and "sequential" do not mean the same thing in every product. Some vendors use "power" for a mode that already dials several lines per agent. The comparison between one line and several simultaneous lines for the same agent is covered in sequential or parallel dialler; the question here is different: whether the system can connect someone who answers when no agent is free.
Ask in writing how many attempts can be in progress per free agent and what happens if more people answer than there are agents available. If the answer is "it never happens", the mode is progressive, whatever it is called.
Abandoned calls, silent calls and their rate
An abandoned call is one that a person answers but the system cannot pass to an agent, so it hangs up or plays a message. A silent call is the same situation without a message: the person answering hears nothing and does not know who was calling. It can also be caused by an answering machine detector that mistakes a person for a machine.
Ofcom, the UK regulator, calculates the rate per calendar day and per campaign or call centre: abandoned calls divided by the sum of abandoned calls and calls answered by a person and connected to an agent. Unconnected attempts and calls to answering machines are excluded from the calculation. Do not confuse this rate with abandonment in an inbound queue, where the person hanging up is the customer who was waiting.
Fictitious example: ten agents and a 25% contact rate
Invented data and a simplified model. Ten agents, a person answers 25% of attempts, each conversation lasts 4 minutes and the wrap-up afterwards 1 minute. In power mode, each unanswered attempt takes 30 seconds of agent time; we do not count the ringing before calls that are answered.
- Power: for each contact there are on average three failed attempts. The cycle is 300 + 90 = 390 seconds, so each agent achieves 3,600 / 390 = 9.2 conversations and 36.9 attempts per hour.
- Ideal predictive: the agent spends time only on contacts, 300 seconds each, that is 12 conversations per hour. Feeding them requires 48 attempts per agent and 480 for the team.
| Scenario | Attempts per hour | People who answer | Handled by agents | Abandoned | Abandonment rate |
|---|---|---|---|---|---|
| Power | 369 | 92 | 92 | 0 | 0% |
| Predictive, matched to capacity | 480 | 120 | 120 | 0 | 0% |
| Pace slightly too high | 500 | 125 | 120 | 5 | 4.0% |
| Pace far too high | 560 | 140 | 120 | 20 | 14.3% |
| Matched, but the contact rate rises to 30% | 480 | 144 | 120 | 24 | 16.7% |
Check with the formula above: 5 / (5 + 120) = 4.0%; 20 / (20 + 120) = 14.3%; 24 / (24 + 120) = 16.7%. The matched predictive scenario gives 30% more conversations than power dialling (120 versus 92), but the last row shows the risk: if the list answers more often than expected, the same pace generates abandonment without anyone changing anything.
The model treats calls as a continuous flow. In reality answers arrive irregularly, so even the "matched" pace will produce some abandonment if it leaves no margin. With ten agents, two extra answers in the same minute already weigh heavily.
What the rules say in the United Kingdom and in Spain
Ofcom's persistent misuse policy, published on 20 December 2016 and applicable from 1 March 2017, is on its page about silent and abandoned calls. Its main points:
- Silent calls are the top enforcement priority.
- It no longer sets a maximum rate: the 3% in the 2010 policy was a criterion for prioritising cases, and Ofcom states that it was never a permitted margin.
- The message on an abandoned call should identify the caller, explain the attempt, give a basic rate number to ask not to be called again and contain no marketing. Ofcom considers whether it starts as quickly as possible and within no more than 2 seconds.
- Calling again within the following 72 hours without guaranteeing an available agent aggravates the case.
- Letting the phone ring for less than 15 seconds or withholding the calling number also aggravates the harm.
In Spain, article 66.1 of Law 11/2022 recognises the right not to receive automated calls without human intervention for commercial purposes without prior consent, and not to receive unwanted commercial calls unless there is consent or another legal basis under article 6.1 of the GDPR. AEPD Circular 1/2023 requires, among other safeguards, that each call begins by stating the identity of the company, the commercial purpose and the right to object. The rules cited do not set a Spanish abandonment rate; do not apply the British percentage as if it were a Spanish rule. A silent call cannot provide that information, and if you plan to use a recorded message, ask your adviser whether it falls under the automated calls provision.
In addition, the Resolution of 14 April 2026 allocates the 400 range to commercial calls by companies covered by Law 10/2025. Those numbers can only make outbound calls and cannot receive calls. If someone wants to call back to object, they will need another channel. Confirm with your operator whether your company is obliged to use it.
When each mode fits
| Situation | Recommended mode | Reason |
|---|---|---|
| One to five agents | Power | Few agents free at the same time; the forecast fails easily |
| Short list or recent enquiries | Power | Each contact is worth more than the minutes saved |
| Conversations that require preparing the record | Power | The agent needs to see the context before the person answers |
| Large team, large list and stable contact rate | Evaluate predictive | The saved waiting time may pay off if abandonment is measured every day |
| Vendor that does not report abandonment per campaign and day | Power | Without that figure you cannot demonstrate control |
Before loading the list, check it with the guide to preparing a CSV for the dialler and apply the do-not-call exclusions.
Checks before switching on a predictive dialler
- Recalculate the example above with your own data: agents, real contact rate, talk time and wrap-up.
- Ask for a daily report per campaign with attempts, answered calls, calls connected to an agent, abandoned calls and silent calls.
- Check that there is a configurable abandonment limit and that the system slows down as it approaches it.
- Use your own test number to hear what someone who answers with no free agent hears.
- Verify that an abandoned number is not redialled in predictive mode until an agent is guaranteed.
- If you cannot meet points 2 to 5, stay with power dialling.
Sources and limitations
Documentary review: . Content type: Documentation-based comparison.
Linked sources describe the terms and capabilities each provider publishes. Examples that use fictional data are labelled in the text.
- using the Aircall Power Dialersupport.aircall.io
- Sinch predictive parametersdocs.cc.sinch.com
- silent and abandoned callswww.ofcom.org.uk
- article 66.1 of Law 11/2022www.boe.es
- AEPD Circular 1/2023www.boe.es
- Resolution of 14 April 2026www.boe.es
Official sources, explained calculations and clearly labelled examples. Read about our methodology and use of AI in writing.