Reference guide · migration-hosting · Published 2026-08-16 · 4 min read
What a hosting SLA actually guarantees
Hosting SLA guide: what uptime percentages really cover, credits and exclusions, maintenance windows, and how to check the guarantee you are sold.
- ·The real guarantee
- ·What the fine print carves out
- ·Claim a credit
99.9% is not a promise about your site
A hosting SLA (service level agreement) is a contract about the host's services, not a guarantee that your site never goes down. The famous "99.9% uptime" figure describes the host's network and infrastructure availability in a given month, calculated on a narrow list, and the compensation for failure is a credit on your bill, not cash and not a fix. Understanding an SLA means reading what it covers, what it excludes, and how to claim the credit, before the outage, not during it.
What a real SLA says
| Clause | What it usually says | What to look for |
|---|---|---|
| Uptime percentage | 99.9% (about 43 minutes downtime/month), 99.95% (about 22 min) | The ceiling, and whether it applies to a whole year or a month, and to which component |
| Covered services | The network, the control panel, the platform | Whether your app's own crash is covered (it is not) |
| Exclusions | Maintenance windows, third parties, DNS, DDoS, your own traffic | Whether the measurement excludes the moments you care about |
| Credit | A percentage of your monthly fee after a threshold breach | Whether it requires you to ask, or is applied automatically |
A single "99.9% guaranteed" without a measurement point is marketing, not an SLA. The measuring tool is your own uptime monitor, and the SLA's own definition of a "downtime event" is the number that decides whether you ever get a credit.
Read the exclusions first
The exclusions are where an SLA is actually defined. Common carve-outs that shrink the guarantee to nothing:
- Maintenance windows: most hosts reserve the right to take the service down for 30-60 minutes a month (or more) for maintenance, and those do not count against the percentage. Verify the maintenance windows have to be posted in advance.
- The platform, not your host: DDoS, DNS, and link failures at the upstream provider are usually excluded; a host with a thin edge has an SLA that excludes exactly the failures you would see.
- Your own dependencies: the guarantee does not cover a broken plugin, a full disk, or a misconfigured CMS that 500s, even when it looks the same as an outage to a visitor.
- "Best effort" in a clause is the polite form of "no guarantee". A cheaper plan with "Best-effort SLA" has no contract at all.
The credit math
Even a clean SLA is a credit, not a refund:
- Typical payment is a percentage of the month's fee. 99.9% breach usually pays 5-10% of one monthly charge, far less than the lost revenue during the outage.
- Credits are subtracted from the *next* bill, and the clock to claim is often 30 days after the incident.
- The host decides the measurement; your uptime monitor data is evidence, not their book.
If the SLA is the basis of your "managed hosting" decision, the realistic reading is: uptime is a hygiene check, not a purchasing guarantee. What the SLA does buy is the *right* to leave: a host that repeatedly breaches a real SLA lets you break the contract without a lock-in penalty, which is the most valuable clause most people never claim.
What to check before a host is your SLA buddy
- Whether the guarantee matters for your site: a brochure site versus a booking platform changes whether a credit is worth the effort of claiming it.
- Which availability figure they promise and which services it covers, in writing.
- The exclusions, precisely, so an outage you actually experienced is one they credit.
- The alerting and monitoring you do yourself: to hold them to the SLA you need independent timing of the outage (an external monitor, not their status page).
The operational half of the story, how you detect an outage and get back up, is the uptime monitor article; the plan-side of "what do I upgrade to" is the hosting upgrade reference. The two together cover the contract and the practice of keeping a site up.