Developer Tools
SLA Uptime Calculator
Convert any SLA uptime percentage to allowed downtime per year, quarter, month, week, and day. Inverts to find achieved uptime from observed downtime.
Calculation mode
Enter a target uptime, see the allowed downtime.
Common SLA presets
Month basis
Result
Allowed downtime per period
99.9% uptime
Per day
24 hours
1 minute, 26.4 seconds
Per week
7 days
10 minutes, 4.8 seconds
Per month
30 days
43 minutes, 12 seconds
Per quarter
90 days
2 hours, 9 minutes, 36 seconds
Per year
365 days
8 hours, 45 minutes, 36 seconds
Reference table
Allowed downtime by SLA percentage
Click any row to load that SLA into the calculator.
| SLA | Per year | Per quarter | Per month | Per week | Per day |
|---|---|---|---|---|---|
| 90%One nine | 36 days, 12 hours | 9 days | 3 days | 16 hours, 48 minutes | 2 hours, 24 minutes |
| 95% | 18 days, 6 hours | 4 days, 12 hours | 1 day, 12 hours | 8 hours, 24 minutes | 1 hour, 12 minutes |
| 99%Two nines | 3 days, 15 hours, 36 minutes | 21 hours, 36 minutes | 7 hours, 12 minutes | 1 hour, 40 minutes, 48 seconds | 14 minutes, 24 seconds |
| 99.5% | 1 day, 19 hours, 48 minutes | 10 hours, 48 minutes | 3 hours, 36 minutes | 50 minutes, 24 seconds | 7 minutes, 12 seconds |
| 99.9%Three nines | 8 hours, 45 minutes, 36 seconds | 2 hours, 9 minutes, 36 seconds | 43 minutes, 12 seconds | 10 minutes, 4.8 seconds | 1 minute, 26.4 seconds |
| 99.95% | 4 hours, 22 minutes, 48 seconds | 1 hour, 4 minutes, 48 seconds | 21 minutes, 36 seconds | 5 minutes, 2.4 seconds | 43.2 seconds |
| 99.99%Four nines | 52 minutes, 33.6 seconds | 12 minutes, 57.6 seconds | 4 minutes, 19.2 seconds | 1 minute | 8.6 seconds |
| 99.995% | 26 minutes, 16.8 seconds | 6 minutes, 28.8 seconds | 2 minutes, 9.6 seconds | 30.2 seconds | 4.3 seconds |
| 99.999%Five nines | 5 minutes, 15.4 seconds | 1 minute, 17.8 seconds | 25.9 seconds | 6 seconds | 0.9 seconds |
| 99.9999%Six nines | 31.5 seconds | 7.8 seconds | 2.6 seconds | 0.6 seconds | 0.1 seconds |
Year is 365 days, quarter is 90 days, week is 7 days, day is 24 hours. Month uses your selected basis above.
Formula
allowed downtime = (1 − uptime%/100) × period seconds
achieved uptime% = (1 − downtime / period) × 100
A "nine" is shorthand for the count of leading nines in the SLA. 99.9% is three nines, 99.99% is four nines, 99.999% is five nines. The downtime budget falls by a factor of ten with each extra nine.
How to use
- Pick a mode: From uptime % to start with an SLA percentage, or From downtime to start with an observed outage window.
- Type the value: a percentage like 99.9, or a downtime number with its unit (seconds, minutes, hours, or days) per chosen period.
- Pick a month basis if you need to match a specific contract: 30 days (AWS billing), 30.4375 days (calendar average), or 31 days (upper bound).
- Read the allowed downtime per year, quarter, month, week, and day, and the achieved uptime percentage at the top of the result panel.
- Use the preset buttons (90%, 99%, 99.9%, up to six nines) to jump between common SLA tiers, or click any row in the reference table to load it.
- Use Copy on any single cell, or Copy summary to grab the full breakdown for a runbook, contract review, or incident report.
About this tool
SLA Uptime Calculator turns any service level agreement uptime percentage into the maximum allowed downtime across every reporting window your contract is likely to reference: per year, per quarter, per month, per week, and per day. Type a target like 99.9% and the tool shows that you can be down at most 8 hours, 45 minutes, 56 seconds in a year, 43 minutes, 49.7 seconds in a month, and roughly 10 minutes, 4.8 seconds in a week. Type 99.99% (four nines) and that budget collapses to 52 minutes, 35.7 seconds per year. Type five nines (99.999%) and you have a 5 minutes, 15.6 seconds annual budget. A second mode inverts the formula: paste in a real observed downtime, like '2 hours per month', and the tool reports the achieved uptime percentage so you can check whether a vendor met their SLA or argue for service credits. The month basis is configurable because contracts disagree: AWS, Azure, and most cloud SLAs measure monthly availability against a fixed 30-day month, so that is the default; switch to 30.4375 days (the calendar year average of 365.25 divided by 12) when you need to match a contract written against 'a calendar month', or switch to 31 days when you want a conservative upper bound. Common nine presets cover 90% through 99.9999% in a single click, and a full reference table renders the allowed downtime for ten different SLA tiers across every period at once, so the entire 'nines' cheat sheet is available without leaving the tool. The formula bar shows the exact math (allowed downtime equals (1 minus uptime over 100) times period seconds, and the inverse) so the calculation is auditable. All arithmetic runs locally in your browser, no values are sent to a server, and the result panel includes copy buttons for every period plus a copy summary button for pasting the full breakdown into a runbook, an incident report, a procurement comparison, an SLA negotiation email, or a status page footnote. Useful for cloud and SaaS vendor evaluation, on-call playbooks, error budget planning for SRE teams, incident postmortems, status page disclosures, hosting plan comparisons, contract review, internal service tiering, and any conversation that turns on the difference between three nines and four nines.
Free to use. Works in your browser. No signup, no login.
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