Downtime Calculator
A promise turned into minutes — what the target allows, what you spent, and what is still yours to lose.
Downtime Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- One window, one target — no tiered credit schedules
- Minutes resolution
In short: A 99.9% promise on a 30-day window is 0.1% of 43,200 minutes: 43.200000 min for the whole period. Spend 12 and 31.200000 min remain — more than half, which is healthy. The same promise at five nines would have allotted 0.432000 min, about 26 seconds; targets are promises about arithmetic before they are promises about uptime.
Formula
allowance = (100 − target)% × window × 1,440 ··· left = allowance − spent
Every availability target is a downtime budget in disguise: subtract the target from 100 and multiply by the minutes in the window. The remainder is what you may still spend — and when it runs out, the contract's credit clause is awake. This page runs the promise forward from a target; the uptime page runs history backward from observed minutes.
Worked Example
- Enter the availability target you promised.
- Set the window the promise covers.
- Enter the downtime already spent.
- Read what is left before the clause wakes.
Defaults: 99.9% over 30 days, 12 min spent → 43.200000 min of allowance, 31.200000 left. Drive the spend to 50 → past the promise by 6.800000 min.
Strengths & Limits Of This Model
Where this engine is strong
- The promise shown as arithmetic, not adjectives
- Over-budget door names the consequence
Where it stops
- No credit schedule modeling — contracts differ
Practical Use Cases
Mid-window checks
is the month still winnable
Contract reviews
what the nines really buy
Change freeze calls
when to stop shipping
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.
Downtime Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How much downtime does 99.9% allow?
It depends only on the window: 99.9% leaves 0.1% for incidents, so a 30-day month allows 43.200000 min, a 28-day window 40.320000 min, and a year 525.6 minutes — about 8.76 hours. The page computes the allowance from whatever window the promise names.
How do I know if my remaining budget is healthy?
Compare the spend to halfway through the window: past half the minutes with less than half the allowance left is a trend, not bad luck. The verdict card names the state — healthy, tightening, at the line, or over — so the change-freeze call is arithmetic, not mood.
What happens when the budget runs out?
Two things at once: the contract's service-credit clause becomes payable, and internally the right move is freezing risky releases until reliability recovers. The page names both because the credit is the cheap part — trust is the expensive one.
Is a five-nines promise reasonable?
Five nines on a month is 0.432000 min — about 26 seconds for the whole period. That is a single fast blip; most real incidents eat it in one shot. Promise nines your architecture has already demonstrated, with margin for the incidents you have not met yet.
Why 1,440 in the formula?
Minutes per day: 24 hours times 60. The window in days times 1,440 gives the denominator everything else compares against. The page shows the arithmetic on the budget card so the allowance can be checked by hand.
Does the target apply to measured or excluded downtime?
Contracts usually exclude scheduled maintenance and sometimes force-majeure events — read the exclusions before feeling rich in minutes. The budget here prices every minute a user could not use the service, which is the honest denominator.
How does this relate to an error budget?
Same idea, different units: the error budget counts failed requests against a request allowance, this page counts minutes against a time allowance. Teams that measure both usually find the request budget moves first — partial failures burn errors long before anyone declares downtime.
What is the difference between this and the uptime page?
Direction. Here a target produces an allowance and you subtract the spend; there, observed minutes produce a percentage. Run both on the same window and the two answers meet at the same line — the promise kept or broken.