Error Budget Calculator

Turn an SLO and a time window into the downtime budget you can spend, then subtract downtime already used to see what remains. Calculates in your browser.

Error budget remaining

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Total budget-
Used-
Remaining (% of budget)-

Show the math

The error budget is the downtime an SLO permits over a period, what you can "spend":

budget = period × (1 − SLO ÷ 100)

For a 99.9% SLO over 30 days the budget is about 43 minutes. Subtract the downtime already used to see what is left; a negative remaining means the SLO has been breached. Calculated entirely in your browser.

What this does

An error-budget calculator turns an SLO and a time window into the downtime you can spend, then subtracts what is already used.

How to use it

  1. Enter your SLO.
  2. Enter the time window.
  3. Enter downtime already used.
  4. Read the remaining budget.

How it works

The budget is the unreliability you can afford before breaching the target. A negative remaining means the SLO has been breached.

error budget = window × (1 - SLO)

Understanding your result

The error budget is the unreliability you are allowed to spend before breaching the SLO, so a healthy remaining balance is permission to ship and take risks, while a near-zero or negative balance is a signal to freeze changes and stabilise. Use it to balance feature velocity against reliability rather than treating every minute of downtime as a crisis.

Example

99.9% over 30 days gives about 43 minutes of error budget.

Sources & methodology

Last updated .

Frequently asked questions

What is an error budget?

It is the amount of downtime an SLO allows over a period, the unreliability you can afford before breaching the target. For 99.9% over 30 days it is about 43 minutes.

What does a negative remaining mean?

It means more downtime has been used than the budget allows, so the SLO has been breached for the period.

Is anything sent to a server?

No. The budget is calculated entirely in your browser.