NetTools

Uptime/Downtime Calculator

Turns an SLA percentage like '99.9%' into a concrete number of minutes you can actually be down.

Uptime SLA (%)

Allowed downtime/year (min)

525.96

The classic 'nines' — 99.9% ('three nines') allows about 8.77 hours of downtime per year; 99.99% ('four nines') allows about 52.6 minutes.

Allowed downtime/month (min): 43.83

What you entered

Uptime SLA (%): 99.9

1
Allowed downtime fraction
1 − 99.9%= 0.1%
2
Downtime minutes per year
0.1% × 365.25 × 24 × 60= 525.96 min/yr

Result

Allowed downtime/year (min): 525.96

A 99.9% SLA allows 525.959999999942 minutes of downtime per year (about 43.829999999995174 minutes/month).

Downtime allowed by each uptime SLA

Every nine you add cuts allowed downtime by a factor of ten. This is the table behind every SLA negotiation.

Uptime	Downtime per year	Downtime per month
90%	52,596.0 min (36.5 days)	4,383.0 min
95%	26,298.0 min (18.3 days)	2,191.5 min
99%	5,259.6 min (3.7 days)	438.3 min
99.5%	2,629.8 min (1.8 days)	219.2 min
99.9%	526.0 min (8.8 hours)	43.8 min
99.95%	263.0 min (4.4 hours)	21.9 min
99.99%	52.6 min	4.4 min
99.999%	5.3 min	0.4 min

Based on a 365.25-day year. Note that 99.99% leaves only 4.4 minutes a month, which is less time than most deploys take, so that tier demands zero-downtime deployment rather than just good hardware.

Each additional 'nine' is a big jump

Going from 99% to 99.9% cuts allowed downtime from about 3.65 days/year to under 9 hours/year — each additional nine of uptime typically requires disproportionately more engineering effort and cost to achieve.

SLA math vs. real incident tracking

This calculates the theoretical downtime budget an SLA allows — actual incident tracking (counting real outages against that budget) is a separate operational practice, not something this simple calculator does.

Frequently asked questions

Our SLA promises 99.9% uptime — how much downtime is that per month?

About 43.8 minutes per month, or 8 hours and 46 minutes per year. That sounds generous until you realize a single bad deployment or database failover can burn the entire monthly budget in one incident.

What's the difference between 99.9% and 99.99% uptime?

A factor of 10 in allowed downtime. 99.9% allows about 8.8 hours/year; 99.99% allows only 52.6 minutes/year. Each additional 'nine' typically requires disproportionately more engineering investment — redundant systems, automated failover, multi-region deployments.

Does scheduled maintenance count against uptime SLAs?

It depends on the SLA's wording. Many SLAs explicitly exclude planned maintenance windows. Others count all downtime regardless of cause. Read the specific SLA terms carefully — the definition of 'downtime' often matters more than the percentage.