95th Percentile Billing Explained: How Burstable Bandwidth Is Charged
Most IP transit and data-centre bandwidth contracts are “burstable”: you commit to a base rate, can use more when you need it, and are billed on the 95th percentile of your usage. It is a fair model — but only if you understand how it is calculated.
The calculation
- The provider samples your port usage every five minutes for the whole month — roughly 8,640 samples in a 30-day month.
- The samples are sorted from highest to lowest.
- The top 5% are discarded — about 432 samples, or 36 hours of peaks.
- The highest remaining value is your billable rate.
Inbound and outbound are measured separately, and the higher of the two is usually billed.
What this means in practice
- Short spikes — a few hours a month — are free.
- Sustained high usage for more than about a day and a half in total will set the bill.
- Usage above your commit is billed at the burst rate, often higher than the committed rate.
Keeping the bill predictable
- Graph your own five-minute usage and calculate the 95th percentile mid-month.
- Schedule large transfers and backups so they do not run for days at peak rate.
- Right-size your commit each year: a higher commit at a lower unit price is often cheaper than paying burst.
We provide transparent 95th-percentile reports with every IP transit port. Ask us to review your usage.
