Uptime Calculator
Observed downtime becomes an availability number — the nines it earns, and the pace it projects.
Uptime Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- One window at a time — no incident clustering
- Minutes resolution on observed downtime
In short: Thirty minutes down in a 30-day window is 43,200 minutes of wall clock, so availability reads 99.930556% — between three and four nines. The same window at five nines would have allotted 0.432 min in total. At this pace a year spends 365 min — about 6 h 5 min of downtime, which is what the number actually promises.
Formula
availability = (1 − downtime ÷ minutes in window) × 100
Availability is one subtraction wearing nines: total minutes in the window, minus what you spent, over the whole. The nines ladder makes the number brutal — each extra nine divides the allowance by ten, so five nines on a month is 25.92 seconds, all in. The pace projection extends the window honestly: the same ratio for a year, which is the figure your users actually experience.
Worked Example
- Enter the minutes the service was actually down.
- Enter how many days the measurement covers.
- Read the availability and its nines.
- Check the yearly pace before celebrating a month.
Defaults: 30 min in a 30-day window → 99.930556%. Drive the downtime to 0 → 100.000000% and the pace card says so honestly. A 5-minute month reads 99.988426%.
Strengths & Limits Of This Model
Where this engine is strong
- Nines ladder computed on the exact window
- Yearly pace named in wall-clock units
Where it stops
- No weighting by traffic at the time of the outage
Practical Use Cases
Incident reviews
the month in one number
Vendor tracking
what the provider really delivered
Capacity talks
pace projected to a year
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Uptime Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How do I calculate uptime percentage?
Divide the minutes the service was down by all minutes in the window, subtract from one, multiply by 100. Thirty minutes down in a 43,200-minute month is 99.930556%. The window is yours to pick — 7, 28, 30 or 365 days all work here.
What do the nines mean?
Each nine is another decimal place of availability: 99.9% allows 43.2 minutes down in a 30-day month, 99.99% allows 4.32, and 99.999% allows 0.432 — about 26 seconds. Every extra nine divides the allowance by ten, which is why each one costs real engineering money.
How much downtime does 99.9% allow per year?
A 365-day year holds 525,600 minutes; 0.1% of that is 525.6 minutes — about 8.76 hours. The page projects your observed pace to that year so a good month is not mistaken for a good year.
Is 100% uptime a real number?
Zero measured downtime gives 100.000000%, and the page prints it — with the honest caveat that a window is a sample, not a guarantee. The pace card treats a clean window as exactly that: untouched, not incorruptible.
Should I use a 28-day or 30-day window?
SRE practice favors rolling 28-day windows because they ignore calendar quirks and never reset on the first of the month. Whichever you pick, measure the same window as whoever you are comparing against — the minutes in the denominator move the answer.
How does this differ from the downtime page?
This page reads history: observed minutes become a percentage. The downtime page reads the promise: a target becomes an allowance of minutes, and what is left of it. Same two numbers, opposite directions — measurement versus budget.
Does scheduled maintenance count as downtime?
Only if your users could not use the service — the number does not care why it was down. Contracts usually exclude scheduled windows; that is a paperwork exclusion, not an experience one, and this page prices the experience.
What is a good pace projection?
One that beats your published promise with margin. A 99.9% promise spends 525.6 minutes a year at exactly budget; a healthy operation wants its measured pace well under that, because incidents cluster and the worst month of the year decides what users remember.