MRR is what your customers have agreed to pay you per month from now on, the monthly value of all active subscriptions.
MRR = sum over all counted subscriptions of (price × quantity, normalised to one month, minus active recurring discounts)
A yearly plan of €1,200 contributes €100 of MRR, a plan billed every six months a sixth of its price. One-off charges, setup fees, taxes and usage that is billed in arrears are not recurring and are left out.
MRR is a property of the subscription, not of an invoice. Read from invoice amounts, a plan change in the middle of a billing period shows up as a spike and a dip, because the invoice contains a prorated line.
sumwerk computes MRR from the state of each Stripe subscription. A trial counts from its first payment, a past-due subscription counts while Stripe still retries and is flagged as at risk, a paused one does not count.
A restricted, read-only key is all it takes. The first import runs in a few minutes; every number you see opens into the customers and Stripe references behind it.