A wholesale rate is quoted per minute, but you are not billed per minute. Each call is rounded up to a billing increment, and a minimum duration can apply on top of that. Two routes with the same headline rate can cost very different amounts once short calls are counted. This guide explains the notation, works through the math with real durations, and covers the prepay, postpay, and commitment terms that come with them.
How a billing increment works
Billing increments are written as minimum/increment. The first number is the shortest duration a call is billed for. The second is the step size after that, and every call is rounded up to the next whole step.
- 60/60: every call is billed for at least 60 seconds, then in 60-second steps.
- 30/6: at least 30 seconds, then in 6-second steps.
- 6/6: no real minimum beyond 6 seconds, then in 6-second steps.
- 1/1: billed per second, with no rounding beyond the second.
The formula is: billed seconds = the larger of the minimum and the call duration rounded up to the next increment. A 13-second call on 6/6 is rounded up to 18 seconds, because 13 divided by 6 is 2.17, and the next whole step is 3 steps of 6.
Worked example: the same calls on four increments
The table shows billed seconds for four call durations on each increment. The durations are chosen to show where the increments diverge.
| Call length | 60/60 | 30/6 | 6/6 | 1/1 |
|---|---|---|---|---|
| 5 seconds | 60 s | 30 s | 6 s | 5 s |
| 13 seconds | 60 s | 30 s | 18 s | 13 s |
| 20 seconds | 60 s | 30 s | 24 s | 20 s |
| 61 seconds | 120 s | 66 s | 66 s | 61 s |
On a 5-second call, 60/60 bills 60 seconds, which is twelve times the talk time. That gap is why a route with a low rate can cost more than a higher-rate route once short calls are counted. The 61-second row shows the opposite effect: one extra second on 60/60 doubles the billed time.
Predictive-dialer traffic can include many short answered calls, so the increment often matters more than it does for a phone conversation. The earlier guide on wholesale voice termination covers how these increments fit into route selection.
Matching the increment to your traffic
The right increment depends on your average call duration (ACD). Compare the increment against the duration you expect to see, not against a headline rate.
- Long conversations (ACD well above 60 seconds): the difference between increments is small, so the rate usually decides the choice.
- Mixed or short traffic (ACD under about 60 seconds, common in predictive dialing): finer increments such as 6/6 or 1/1 can reduce billed time substantially.
- Attempts that connect and drop quickly: a 60/60 minimum bills the full minute for every one of them.
Ask for the increment in writing for each route in the rate deck. Some providers state one increment for all destinations, while others vary it by route or prefix. Do not assume the increment from one route applies to another.
Prepay, postpay, and commitments
Billing increments decide how each call is measured. Payment terms decide when you pay and what happens if the account runs short. Three models are common:
- Prepay: you load a balance before sending traffic. Calls are blocked when the balance runs out. Prepay limits your exposure to the provider and is common for new accounts.
- Postpay: usage is invoiced after a billing period, usually subject to a credit limit set when the account is approved. Postpay suits higher-volume accounts, but it requires credit review, and an unexpected traffic spike can reach the credit limit quickly.
- Minimum top-up or minimum commit: a minimum amount you agree to load or spend. A minimum top-up is a single payment. A minimum commit is a total over a period, and shortfalls may be billed.
Before signing, get the answers in writing: the credit limit or prepay floor, what happens when a balance or limit is reached (calls blocked, or traffic continues with a bill), the invoice cycle, the payment terms, and how a shortfall against a commitment is handled.
Illustrative cost comparison
The numbers below are an illustration, not a quote. Assume a rate of $0.01 per minute and 1,000 answered calls, each 13 seconds long.
- On 60/60: each call bills 60 seconds, so 1,000 calls bill 16.7 hours, or about $10.00.
- On 6/6: each call bills 18 seconds, so 1,000 calls bill 5 hours, or about $3.00.
The rate is the same in both cases. The increment alone changes the cost by about 70 percent on this traffic. This is why the rate deck should always be read with the increment column.
Questions to ask a wholesale provider
- Which billing increment applies to each route, and does it differ by destination?
- Is there a minimum billed duration, and is it the same for every route?
- Is the account prepay or postpay, and what is the credit limit or balance floor?
- What happens at the limit: are calls blocked, or does traffic continue and invoice later?
- Is there a minimum commit or top-up, and how is a shortfall billed?
- How are rate and increment changes notified, and how far in advance?
Next steps
Once you know the increment, check whether the route quality supports the traffic. The guide to ASR, ACD, PDD, and MOS explains the measurements buyers compare on. For a route-by-route comparison of rates, see CC routes pricing.