What does 99.9% uptime actually mean?

99.9% uptime (three nines) allows approximately 8 hours 45 minutes of downtime per year, 43 minutes and 49 seconds per month, or just 1 minute and 26 seconds per day.

How is the downtime calculated?

Downtime = (1 - uptime_fraction) × period_in_minutes. For example, 99.9% uptime means 0.1% downtime, so per year: 0.001 × 525,960 minutes = 525.96 minutes ≈ 8h 45m.

What is the difference between 99.9% and 99.99%?

99.9% (three nines) allows ~8.7 hours/year; 99.99% (four nines) allows only ~52 minutes/year. Each additional nine reduces downtime by roughly 10x.

How many minutes are in a month?

This calculator uses 30.4375 days per month (365.25 / 12) to account for leap years, giving 43,829.1 minutes per month.

What is an error budget?

An error budget is the amount of downtime your SLA permits. SRE teams track how much of this budget has been consumed to decide when to prioritize reliability work over new features.

Can I enter a custom uptime percentage?

Yes. Type any value between 0 and 100 in the input field. The calculator accepts decimal values like 99.95 or 99.999.

Downtime From SLA Calculator

Name: Downtime From SLA Calculator
Availability: InStock
Author: Nham Vu

Enter an SLA uptime percentage and instantly see the allowed downtime per day, week, month, and year.

SLA Uptime Percentage

Enter the guaranteed uptime from your SLA agreement.

Common SLA Tiers

Custom uptime %

Allowed Downtime Budget

Downtime permitted while staying within the SLA.

Enter a percentage and click Calculate.

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Summary

Enter an SLA uptime percentage and instantly see the allowed downtime per day, week, month, and year.

How it works

Enter your SLA uptime percentage (e.g. 99.9).
The calculator converts the percentage to a downtime fraction (1 - uptime%).
It multiplies that fraction by the total minutes in each time period.
Results are displayed in the most readable unit (seconds, minutes, or hours).
Use the preset buttons to quickly load common SLA tiers.

Use cases

Evaluate whether a cloud provider SLA meets your availability requirements.
Plan maintenance windows within the allowed downtime budget.
Write accurate SLAs for your own hosted services or APIs.
Compare uptime guarantees across vendors side by side.
Calculate error budget for SRE teams practicing SLO-based reliability.
Communicate downtime impact to stakeholders in plain time units.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu