What is an error budget?

An error budget is the allowable amount of unreliability derived from your SLO. A 99.9% SLO implies a 0.1% error budget — roughly 43.8 minutes per month. When that budget is consumed, teams typically halt risky changes until the next window resets.

How is the error budget calculated?

Total window seconds multiplied by (1 - SLO/100) gives allowed downtime seconds. If you enter a current error rate, the tool multiplies that rate by the window length and subtracts it from the total budget to show remaining budget.

What time window should I use?

Monthly windows (30 days) are the most common in SRE practice because they align with on-call rotations and business reporting cycles. Quarterly or yearly windows give teams more room but delay feedback on reliability trends.

What does "current error rate" mean?

It is the fraction of requests or time that is currently failing or degraded, expressed as a percentage. For example, if 0.05% of requests are returning errors, enter 0.05. The tool computes how much of your budget that rate is consuming.

Can I enter an SLO above 100% or below 0%?

No. SLO values must be between 0% and 100% exclusive. Values outside that range are invalid and the tool will show an error.

Error Budget Calculator

Name: Error Budget Calculator
Availability: InStock
Author: Nham Vu

Calculate your SLO error budget — enter a target SLO percentage and time window to see allowed downtime, then subtract your current error rate to see remaining budget.

SLO Parameters

Target SLO (%)

Time Window

Current Error Rate (%) — optional

Percentage of requests or time currently failing. Leave blank to skip budget burn calculation.

Set your SLO and time window, then click Calculate.

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Summary

Calculate your SLO error budget — enter a target SLO percentage and time window to see allowed downtime, then subtract your current error rate to see remaining budget.

How it works

Enter your target SLO percentage, for example 99.9%.
Choose a time window: day, week, month, quarter, or year.
The tool multiplies the window seconds by the allowed failure fraction (1 - SLO%) to get allowed downtime.
Optionally enter your current error rate to subtract consumed budget.
Read the allowed downtime and remaining error budget instantly.

Use cases

Determine how many minutes of downtime are acceptable under a 99.9% monthly SLO.
Track remaining error budget after an incident to decide whether to freeze deployments.
Compare error budget impact across different time windows before committing to an SLO.
Translate abstract SLO percentages into concrete, stakeholder-friendly downtime figures.
Estimate how quickly an ongoing degradation will exhaust the monthly error budget.

Frequently Asked Questions

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