budgetConsumed property
The share of the window's budget used so far. Above 1 is past it.
Null when there is nothing to read -- no source, fewer than two samples, or samples with no request between them -- because an unknown is not a clean month. The last is the one that looks like one: a service that stopped answering sends nothing to count, and 0 consumed would show its budget full for exactly the outage the budget is there to catch.
Implementation
final double? budgetConsumed;