Uptime SLA Calculator
Convert any SLA percentage into the real downtime budget per day, week, month, and year. Pick a preset or enter a custom value. Share the URL or embed the calculator on your own page.
What does an SLA percentage actually mean?
An SLA (Service Level Agreement) percentage tells you what share of time a service is contractually required to be available. The remainder is the budgeted downtime window. The higher the percentage, the smaller the allowed window, and the more expensive the infrastructure required to hit it.
The thing most people get wrong is intuition for the gap between tiers. 99% sounds close to 99.9%, but it is ten times more downtime per year. 99.9% to 99.99% is another 10x. The calculator above makes the gaps concrete by showing per-day, per-month, and per-year time budgets side by side.
Related tools
- Downtime Cost Calculator → Turn your time budget into a dollar impact.
- SLA Credit Calculator → Calculate the refund you are owed when a vendor misses their SLA.
Frequently asked questions
What does 99.9% uptime actually mean in downtime?
99.9% uptime allows up to 8 hours and 45 minutes of downtime per year, which is roughly one full workday. Per month, that is about 43 minutes. Per day, about 1 minute 26 seconds. The SLA percentage is the share of time your service is required to be available, and the rest is the budgeted downtime window. Whether your real downtime is concentrated in one outage or spread across many small incidents, the total against your SLA is what counts.
How is downtime per period calculated from an SLA percentage?
The formula is (100 minus your SLA percentage) divided by 100, multiplied by the seconds in the period. For example, 99.9% over one year: (100 - 99.9) / 100 = 0.001, times 31,557,600 seconds in a year (365.25 days), equals 31,557.6 seconds, or 8 hours 45 minutes 57 seconds. Months use 30.4375 days as the yearly average. The calculator on this page does this math automatically and presents per day, week, month, and year.
What is the difference between 99.9% and 99.99% uptime?
99.9% (three nines) allows about 8 hours 45 minutes of downtime per year. 99.99% (four nines) only allows about 52 minutes per year. The jump from three to four nines is roughly a 10x reduction in allowed downtime. It typically requires multi-AZ deployments, automated failover, and on-call rotation. Five nines (99.999%) allows only about 5 minutes per year, which generally requires multi-region active-active deployments and dedicated SRE staffing. Pick the lowest tier your customers tolerate, do not over-engineer.
What is a good SLA target for a small SaaS?
99.9% is the standard cloud-provider offering and a reasonable target for most B2B SaaS. It signals seriousness without forcing you into multi-region complexity. Going below (99% or 99.5%) is honest if you cannot operationally hit higher, but customers will notice and enterprise buyers will exclude you. Going above (99.99%+) is rarely necessary unless your customers are in finance, healthcare, or industrial systems. Match your SLA to what you can actually verify and pay out on, not what looks impressive.
How accurate is this calculator?
The math is exact, using 365.25 days per year and 30.4375 days per month (the yearly average). The only ambiguity in real SLA contracts is what counts as downtime. Most contracts carve out scheduled maintenance, third-party network issues, and partial functionality. That is a contract-language question, not an arithmetic one.
Can I embed this calculator on my own site?
Yes. Click Embed under the calculator for a copy-paste iframe. The embedded version is chrome-less (no Velprove nav or footer) and links back to the full calculator. Use it on commercial sites without asking.
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