Uptime & SLA Calculator

Turn an SLA uptime percentage into the downtime it actually allows — and back again. Enter a target like 99.9% or 99.999% ("five nines") and see exactly how much downtime you're permitted per day, week, month, quarter and year. Or work in reverse: give it a downtime budget and it tells you the SLA percentage you'd have to hit. Everything runs in your browser, instantly, with nothing sent to a server.

Three modes

• Allowed downtime for an SLA % — pick a common tier (or type a custom percentage) and get a full breakdown by period, plus a side-by-side comparison of every standard SLA tier.
• Required SLA % for a downtime target — say "at most 5 minutes of downtime per month" and it returns the uptime percentage that implies (and the nearest common tier).
• Error budget remaining — enter your SLA and how much downtime you've already burned this period; it shows how much of your error budget is left before you breach.

How the math works

Allowed downtime is simply (1 − uptime%) × period length. At 99.9% uptime the "unavailable" fraction is 0.1%, so over a 365.25‑day year that's 0.001 × 31,557,600 s ≈ 8h 46m. The reverse mode inverts it: uptime% = (1 − downtime ÷ period) × 100.

Two length conventions matter, and this tool uses the same ones as uptime.is and most SRE references:

• Year = 365.25 days (a Julian year), so a quarter is 91.31 days.
• Month = 30 days (the standard flat SLA assumption), week = 7 days, day = 24 hours.

If your contract defines the month or year differently, scale the result accordingly.

Common SLA tiers and their allowed downtime

SLA uptime	Per year	Per month	Per day
99% (two nines)	3d 15h 39m	7h 12m	14m 24s
99.5%	1d 19h 49m	3h 36m	7m 12s
99.9% (three nines)	8h 45m 58s	43m 12s	1m 26s
99.95%	4h 22m 59s	21m 36s	43s
99.99% (four nines)	52m 36s	4m 19s	9s
99.999% (five nines)	5m 16s	26s	864ms

Each extra nine cuts your downtime budget by roughly 10×, which is why the jump from 99.9% to 99.99% — and again to 99.999% — gets expensive fast in engineering and redundancy terms.

What is an error budget?

An error budget is the flip side of an SLA: the total downtime you're allowed to spend in a period without breaking your commitment. A 99.9% monthly SLA gives you 43m 12s of budget; the budget mode tracks how much you've used and how much remains, so you can decide whether it's safe to ship a risky change or ship at all.

Is my data private?

Yes. All calculations happen locally in your browser — no percentages, downtime figures or budgets are uploaded anywhere.