A/B Testing SLA Annual Formula
Learn how annual downtime allowance, effective availability, and remaining downtime budget are calculated for an A/B testing service-level agreement.
This calculation converts an annual availability target into a downtime allowance and compares that allowance with recorded scheduled and unplanned downtime. It helps teams estimate whether an A/B testing service remains within its stated annual SLA target.
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Effective Availability
Where:
Start with every hour in the measurement period, subtract all downtime that counts under the SLA, then divide the remaining available hours by total hours and convert the result to a percentage.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| daysInPeriod - Days in measurement period | The number of calendar days covered by the annual SLA measurement period. | days |
| scheduledDowntime - Scheduled downtime | Planned maintenance hours that count as unavailable under the SLA terms. | hours |
| unplannedDowntime - Unplanned downtime | Outage hours affecting the A/B testing service that count toward the SLA. | hours |
| slaTarget - Annual SLA target | The minimum availability percentage specified for the measurement period. | percent |
| annualServiceHours - Total service hours | All hours in the selected measurement period before subtracting downtime. | hours |
| totalDowntime - Total counted downtime | The sum of scheduled and unplanned downtime included in the calculation. | hours |
Step-by-Step Calculation
Calculate total service hours
Convert the measurement period from days into hours. A 365-day period contains 8,760 hours.
annualServiceHours = daysInPeriod * 24
Calculate the SLA downtime allowance
Find the share of time not guaranteed by the availability target and apply it to total service hours.
allowedDowntime = annualServiceHours * (1 - slaTarget / 100)
Add counted downtime
Combine all planned and unplanned downtime that the SLA treats as unavailable service.
totalDowntime = scheduledDowntime + unplannedDowntime
Calculate remaining downtime budget
A positive result means downtime remains within the allowance. A negative result means the allowance has been exceeded.
downtimeBudgetRemaining = allowedDowntime - totalDowntime
Calculate effective availability
Divide the hours remaining available by all hours in the period, then express the result as a percentage.
effectiveAvailability = (annualServiceHours - totalDowntime) / annualServiceHours * 100
Calculate availability variance
Compare achieved availability with the SLA target in percentage points.
slaVariance = effectiveAvailability - slaTarget
Example: 99.9% annual SLA with 5 hours of counted downtime
Total service hours
365 * 24
8,760 hours
Maximum allowed downtime
8760 * (1 - 99.9 / 100)
8.76 hours
Total counted downtime
4 + 1
5.00 hours
Downtime budget remaining
8.76 - 5.00
3.76 hours
Effective availability
(8760 - 5) / 8760 * 100
99.943%
Availability variance
99.943 - 99.9
+0.043 percentage points
Final Result
The 99.9% annual SLA allows 8.76 hours of downtime. With 5.00 hours recorded, effective availability is 99.943% and 3.76 hours of downtime budget remains.
Assumptions
- ✓The SLA is measured over the full number of days entered.
- ✓Availability equals total service time less counted downtime, divided by total service time.
- ✓All entered scheduled and unplanned downtime counts toward the SLA.
- ✓The SLA target is treated as an availability percentage rather than a guarantee of no incidents.
Limitations
- !Actual provider reports may exclude maintenance windows, customer-caused events, third-party failures, or force majeure events.
- !Incident start and end times may be measured differently under the agreement.
- !The calculator does not determine service credits, remedies, or contractual compliance beyond the simple availability estimate.
- !Rounding rules in an SLA can change a result near the target threshold.
Common Mistakes to Avoid
Using 365 days when the contractual measurement period includes 366 days.
Including planned maintenance that the SLA explicitly excludes from downtime.
Leaving out short incidents that count under the provider's measurement rules.
Comparing downtime against a monthly allowance when the agreement is measured annually.
Treating a positive downtime budget as confirmation of contractual compliance without checking exclusions and rounding.
Related Formulas
Frequently Asked Questions
How is annual SLA availability calculated?
Annual availability is total measurement-period hours minus counted downtime, divided by total measurement-period hours, multiplied by 100.
How much downtime does a 99.9% annual SLA allow?
For 365 days, 99.9% availability allows 8.76 hours of counted downtime. The allowance changes with the measurement period.
What does a negative downtime budget mean?
It means entered downtime is greater than the downtime allowance implied by the selected SLA target.
Does scheduled maintenance count as SLA downtime?
It depends on the agreement. Enter scheduled maintenance only when the SLA says it counts toward availability.
Why can effective availability differ from an SLA report?
The agreement may use exclusions, maintenance rules, event definitions, time zones, or rounding methods not represented in this simple calculation.
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