Data caps
Counted on your billing cycle, not the calendar month.
"How much of my allowance is left, and am I going to make it to the end of the cycle" is a question a network monitor should answer. Most of them do not.
Set your cap and tell Pinned the day your carrier's cycle starts. Every total is then counted against that window, so a cycle beginning on the 12th runs from the 12th to the 11th, which is what your bill already does.
The awkward cases are handled rather than ignored. A cycle day of 31 uses 28 February and 30 April, and lands back on the 31st in the months that have one. A cycle should never silently skip a month because the calendar was short.
When you are on course to overrun, Pinned says so in words instead of leaving you to do the arithmetic:
Totals are also kept per network, so you can see how much went over the hotel Wi-Fi and how much went over the phone hotspot, which is usually the one that costs real money. Alerts fire at the cap thresholds you choose, on the same hold-and-cooldown rules as every other alert.
Cycle handling