ToolsError budget calculator
How long will your error budget last?
An SLO below 100% leaves room to fail. This shows how much room, in time and in requests, and how quickly the current burn rate uses it up.
Calculator
Budget
Optional. For a request-based SLO, the number of requests you expect in the window.
Error budget over 30 days
43 min 12 s
43.2 min of full downtime, rounded down to the millisecond.
Burn rate
How much of this window's budget is left.
1 spends exactly the whole budget over the window; 2 spends it twice as fast.
Time until the budget runs out
15 d
At 2× with 100% of a 30-day budget left: (100% × 30 days) / 2.
| Page: 2% of the budget in 1 hourLong window 1 hour, short window 5 minutes | 14.4× |
|---|---|
| Page: 5% of the budget in 6 hoursLong window 6 hours, short window 30 minutes | 6× |
| Ticket: 10% of the budget in 3 daysLong window 3 days, short window 6 hours | 1× |
Method
Budgets, burn rates and alerts.
Budget
Budget = window × (100 − SLO) / 100
A 99.9% SLO over 30 days allows 43 min 12 s of full downtime, or one failed request in a thousand. Time budgets round down to the millisecond, request budgets to a whole request.
Burn rate
How fast the budget is being spent
A burn rate of 1 spends exactly the whole budget by the end of the window. At 2 it runs out halfway through; at 14.4 a 30-day budget lasts about two days.
Time left
Remaining budget / burn rate
Time left = (remaining % / 100) × window / burn rate, assuming the rate stays constant. Real incidents rarely hold a constant rate, so treat it as a warning horizon, not a forecast.
Two windows
Alert when a long and a short window both burn fast
A single window either pages too late or keeps paging after the problem is fixed. The usual pattern (from the Google SRE Workbook, Alerting on SLOs) checks a long window to prove the spend is significant and a short one, a twelfth of its length, to prove it is still happening. Page at 2% of the budget in 1 hour or 5% in 6 hours; open a ticket at 10% in 3 days. The burn rates in the table follow from your window: burn = budget share × window / long window.