95th Percentile Bandwidth Billing Explained: How It's Calculated and How to Read Your Traffic Graph
Data centers and IP transit carriers often bill bandwidth by the "95th percentile", also called 95th percentile or burstable billing. It sounds complicated, but the rule is simple: measure your traffic rate regularly, throw away the busiest 5% of measurements, and bill the highest one that remains. This guide explains how the number is calculated, how it compares with flat-rate ports and monthly transfer plans, and how to read the traffic graph in your server panel.
How the 95th Percentile Is Calculated
- The switch records the traffic rate on your port at a fixed interval, usually every 5 minutes, in megabits per second (Mbps).
- At the end of the month, all samples are sorted from highest to lowest. A 30-day month with 5-minute samples has 8,640 samples.
- The top 5% are discarded: 432 samples, which is about 36 hours of the busiest traffic.
- The highest remaining sample is the 95th percentile, and that is the billed rate.
In practice, short bursts are free. A backup that saturates the port for one hour every night adds up to about 30 hours a month, which is less than the 36 hours that get discarded, so it does not raise the bill. Traffic that stays high for more than about 36 hours in the month does.
A worked example
| Usage pattern | Time at that rate | Effect on the 95th percentile |
|---|---|---|
| Normal traffic around 80 Mbps | Most of the month | Sets the baseline |
| Evening peak at 150 Mbps | 4 hours a day, about 120 hours | Longer than 36 hours, so the 95th percentile lands near 150 Mbps |
| Nightly backup at 900 Mbps | 1 hour a day, about 30 hours | Shorter than 36 hours, so it is discarded |
Inbound, outbound or both?
Providers measure in one of three ways, and your contract will say which:
- Greater of in and out: calculate the 95th percentile for each direction and bill the higher one. This is the most common method.
- Outbound only: common for websites and download servers, where outbound traffic dominates.
- Combined: add in and out for each sample, then take the 95th percentile.
95th Percentile vs Other Billing Models
| Model | What you pay for | Good for |
|---|---|---|
| Fixed port (dedicated / unmetered bandwidth) | A port speed such as 100 Mbps you can use 24/7 | Steady, predictable traffic; easy budgeting |
| Monthly transfer (for example 10 TB) | Total data in GB or TB | Low average usage with occasional spikes |
| 95th percentile (burstable) | A committed rate plus the 95th percentile above it | Large, variable traffic: CDN nodes, IDC resellers, streaming |
The difference between Mbps and data volume is explained in Mbps vs MB/s, bandwidth and monthly traffic.
Reading the Traffic Graph in the IMIDC Panel
Open your server in the client area and go to Server details → Traffic (see the dedicated server control panel guide):
- Blue area: inbound traffic. Teal area: outbound traffic.
- Dashed lines: the 95th percentile of each direction for the selected time range.
- Orange line: the combined 95th percentile used as the billing reference.
- Range buttons (1h to All): the 95th percentile is recalculated for the range you select. Select a full month to compare it with a monthly bill.
- Latest / Average / Max table: if the maximum is far above the 95th percentile, you have short bursts; if the average is close to it, your traffic is steady.
The Live inbound / Live outbound rows in the Bandwidth & Traffic card show the newest sample, refreshed every 30 seconds.
Calculate It Yourself
If you have your own samples, for example exported from your monitoring as one Mbps value per line, the 95th percentile is a one-liner:
# samples.txt: one rate per line (Mbps), e.g. 5-minute averages for a month
sort -n samples.txt | awk '{a[NR]=$1} END {i=int(NR*0.95); if(i<1)i=1; print "95th percentile:", a[i], "Mbps of", NR, "samples"}'To collect your own data on Linux, vnstat gives you a long-term history; Linux server monitoring shows how to install it.
How to Keep the 95th Percentile Down
- Schedule heavy jobs such as backups, syncs and large uploads in one block of less than about an hour a day, not spread across the day.
- Cache and compress: enable gzip or brotli and put static files behind a CDN.
- Find unexpected traffic early: a compromised server sending spam or attack traffic can raise the bill and get IPs blacklisted. See checking whether a Linux server is hacked, and for host nodes finding abusive VPS.
- Rate-limit at the source: cap backup and sync tools, for example
rsync --bwlimit=20000(KB/s).
FAQ
My graph shows a big spike. Will it cost more?
Not if it lasted less than about 36 hours in the month in total, because those samples fall into the discarded 5%. On a fixed-port plan a spike is simply limited by the port speed.
Why does the 95th percentile change when I pick a different range?
It is calculated only from the samples inside the selected range. A billing period is a full month, so compare the monthly value.
The graph is empty
Some switch ports do not report traffic samples. Open a ticket and we will check the collection for your port.
Still stuck after following these steps? Open a support ticket and the IMIDC 24/7 technical team will help. Include the server IP and a screenshot of the traffic graph so we can pinpoint the issue faster.