Error Budget Calculator
See how much of your objective's error budget is left, by events or by time.
In short
Formula: Error budget = Valid events × (1 − SLO); Remaining = Error budget − Bad events. By time: Error budget = Period × (1 − SLO); Remaining = Error budget − Downtime
What this calculator does
The error budget as defined in the SRE workbook: the complement of the objective applied to the population the objective is measured over. The basis is chosen by the user so the budget matches how their objective is written; the two bases are never mixed in one result.
Use it to turn How is your objective measured?, Service level objective, Valid requests in the period, Requests that failed the objective, and the other shown inputs into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this professional & industry calculation.
Inputs and what they mean
- How is your objective measured?
- — Use the same basis your service level objective is written in..
- Service level objective
- — The objective your team agreed. Nothing is assumed about what it should be..
- Valid requests in the period
- — Total requests the objective is measured over..
- Requests that failed the objective
- — Requests counted as bad against the objective so far..
- Length of the period
- — Hours in the objective window..
- Unavailable time so far
- — Minutes counted against the objective so far..
How to use it
- Enter your own figures — the calculator never fills in a rate, price or benchmark for you.
- Press Calculate to see the result.
- Read the formula, variables, assumptions and source below the result before you rely on it.
Formula
Error budget = Valid events × (1 − SLO); Remaining = Error budget − Bad events. By time: Error budget = Period × (1 − SLO); Remaining = Error budget − Downtime.
Inputs used: How is your objective measured?, Service level objective, Valid requests in the period, Requests that failed the objective, Length of the period, Unavailable time so far.
Edge handling: Service level objective is required.; Service level objective cannot be negative.; Service level objective must be no more than 100.; Valid requests in the period is required.; Valid requests in the period cannot be negative..
Worked example
A 99.9% objective over 20 million requests
- Start with How is your objective measured?: events, Service level objective: 99.9, Valid requests in the period: 20000000, Requests that failed the objective: 9000, Length of the period: 720, Unavailable time so far: 20.
- Apply the method: Error budget = Valid events × (1 − SLO); Remaining = Error budget − Bad events. By time: Error budget = Period × (1 − SLO); Remaining = Error budget − Downtime.
- The budget is what the objective you entered permits — not a recommended allowance.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this error budget calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: Google — Implementing SLOs
Last reviewed:
Common questions
Where does this formula come from?
Implementing SLOs — a service level objective is the share of good events among valid events (or of available time in the period); the error budget is the remainder that the objective permits. See the source link on this page.
What kind of calculation is this?
The failures an objective permits over a period, less the failures recorded so far. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
What are its limits?
Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete. A mean over a short period, or over few events, is a weak description of behaviour. A budget for a period says nothing about how quickly it is being spent within that period.
How do I use the Error Budget Calculator?
Enter the required values for How is your objective measured?, Service level objective, Valid requests in the period, Requests that failed the objective, Length of the period, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Error Budget Calculator use?
Error budget = Valid events × (1 − SLO); Remaining = Error budget − Bad events. By time: Error budget = Period × (1 − SLO); Remaining = Error budget − Downtime The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Error Budget Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Formula, source and verification
The failures an objective permits over a period, less the failures recorded so far.
The question it answers: How much error budget does our objective allow, how much is left, and did we meet the commitment in the agreement?
The formula
Error budget = Valid events × (1 − SLO); Remaining = Error budget − Bad events. By time: Error budget = Period × (1 − SLO); Remaining = Error budget − Downtime
- SLO — Service level objective
- (%). The objective the user's team agreed.
- V — Valid events
- (count). Requests the objective is measured over.
- B — Bad events
- (count). Requests counted against the objective so far.
- P — Period
- (h). Length of the objective window, for the time-based form.
- D — Downtime
- (min). Minutes counted against the objective so far.
Units: Counts for the event basis, minutes for the time basis, percentage for the objective.
What kind of calculation this is
Deterministic formula. The same inputs always give the same answer. The maths is fixed and does not depend on judgement.
Method
The error budget as defined in the SRE workbook: the complement of the objective applied to the population the objective is measured over. The basis is chosen by the user so the budget matches how their objective is written; the two bases are never mixed in one result.
Assumptions built into the result
- Mathematical: The figures entered all cover the same measurement period.
- Mathematical: Incidents, changes and requests are counted consistently with the definition the team has written down.
- Mathematical: The objective and the events counted use the same definition of a bad event.
Figures this calculator will never guess for you
- No target, benchmark, industry average or performance band is supplied for any figure.
- A definition is never presented as a goal: the availability formula is not an availability target, and the change failure rate formula is not an acceptable failure rate.
- No burn-rate alert threshold or policy is implied.
Limitations
- Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete.
- A mean over a short period, or over few events, is a weak description of behaviour.
- A budget for a period says nothing about how quickly it is being spent within that period.
Source and version
- Standard or reference
- Google SRE Workbook — Implementing SLOs — Google SRE (Implementing SLOs — a service level objective is the share of good events among valid events (or of available time in the period); the error budget is the remainder that the objective permits.)
- Published source
- Google — SRE Workbook
- Formula version
- Version 1
- Verification
- Reviewed against the cited source on
- How much weight the source carries
- Standards or government
- Applies to
- Currency
- The result is a ratio or index, so it does not depend on currency.
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