SLA Uptime Calculator
SLA uptime calculator: turn an availability target such as 99.9% into the downtime it really allows per day, week, month, quarter and year, then track error-budget burn.
Allowed downtime at 99.9%
This is your error budget - the outage time the SLA permits before you breach it.
- Per day
- 1.4 min
- Per week
- 10.1 min
- Per month (30 d)
- 43.2 min
- Per quarter (90 d)
- 2.2 h
- Per year (365 d)
- 8.8 h
Error budget burn
About SLA Uptime Calculator
The SLA Uptime Calculator converts an availability percentage into the thing people actually argue about: minutes of permitted downtime. Enter a target, or pick a preset from 90% up to five nines, and you get the allowed outage per day, per week, per 30-day month, per 90-day quarter and per 365-day year. Seeing that 99.9% leaves 43.2 minutes a month while 99.99% leaves 4.3 makes the cost of each extra nine concrete before it is written into a contract you then have to meet.
The number only means something once you fix the window and the measurement. An SLA is the contractual promise with a penalty attached; the SLO is the internal target you run against, and it should be stricter, because you want to notice a breach before a customer claims one. Downtime here is computed on fixed 30, 90 and 365-day windows, which is how most contracts are written, but many providers measure a rolling 28-day window instead. Two teams quoting the same percentage against different windows will disagree about whether an outage breached it.
The second panel treats the allowance as an error budget in the SRE sense: the downtime you are permitted to spend, deliberately, on releases and risky changes. Enter the minutes already lost this month and it shows the share of the budget consumed, what remains, and a bar that turns amber past 75% and red once you are over. Read it as a signal rather than a scoreboard: budget left means you can ship, budget exhausted means the next change should be a stabilising one. Everything is computed in the browser, with no figures leaving your machine.
How to use it
- 1Enter your target availability as a percentage, or click a preset from 90% up to 99.999%.
- 2Read the allowed downtime for each period: day, week, 30-day month, 90-day quarter and 365-day year.
- 3Enter the downtime already used this month, in minutes, under Error budget burn.
- 4Read the share of the budget consumed and the time remaining, and watch the bar turn amber past 75% and red when you go over.
- 5Switch presets to compare targets and see what an extra nine would actually cost you in permitted outage.
Common use cases
- -Checking what a 99.9% commitment in a customer contract really allows before you sign it.
- -Tracking how much of this month's error budget a single incident has consumed.
- -Comparing a 99.9% and a 99.99% target to justify the cost of extra redundancy.
- -Setting an internal SLO that is deliberately stricter than the external SLA you have promised.
- -Explaining to a non-technical stakeholder why five nines means minutes per year, not hours.
Frequently asked questions
- How much downtime does 99.9% uptime allow?
- About 43.2 minutes per 30-day month, which works out to 1.44 minutes per day, 10.1 minutes per week, 2.16 hours per 90-day quarter and 8.76 hours per 365-day year. The exact figures depend on the window your contract uses, since a 31-day calendar month allows slightly more than a flat 30-day month.
- What is an error budget?
- The error budget is the unreliability an SLO permits: if your target is 99.9% over a month, the budget is roughly 43 minutes of downtime. Treating it as a resource rather than a failure is the point of the practice popularised by Google's SRE work. Budget remaining means you can take release risk; budget exhausted means the next change should reduce risk instead.
- What is the difference between an SLA, an SLO and an SLI?
- An SLI is the measurement, for example the percentage of successful requests. An SLO is the internal target for that indicator. An SLA is the contract with a customer that attaches consequences, usually service credits, to missing it. Set the SLO tighter than the SLA so you get warning before a breach becomes a commercial problem.
- What does five nines availability mean?
- 99.999% availability, which permits about 5.26 minutes of downtime per 365-day year, 26 seconds per 30-day month and under a second per day. At that level a single unplanned reboot can breach the target for the whole year, so it demands redundancy at every layer, automated failover, and change processes that do not depend on a human noticing quickly.