A 99.9% monthly SLO is a 99.5% weekly SLO

If your SLO or SLA is defined as being calculated over a one-month reporting period, you cannot use that same number when measuring on a daily or weekly basis.

For example, a 99.9% SLO over a 30-day period is equivalent to about 99.5% over a 7-day period:

• A 99.9% SLO allows 43m 49s of unavailability per month.
• This means you can have 10 minutes of unavailability for every week that month.
• It also means you can have 29 days of full availability and 43m of unavailability on the final day of the month.

If you change your reporting period from a month to a week, you then need an SLO which allows up to 43 minutes of unavailability per week. To hit that target, you need an SLO of 99.5% (99.565% to be precise).