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A period is a named stretch of time, and everyone points at the same one. Sep 2026, Q3 2026, FY2025. It has a start date and an end date. That is all it is. Projects are the dated jobs. Invoices are the bills. When a project says September 2026 bookkeeping and an invoice says September 2026, they point at the exact same September 2026. That’s what lets work and billing line up without anyone matching dates by hand.

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Things to know

  • Nobody types periods in. Flows makes each period the first time something needs it, and reuses it after that.
  • One per firm. There is only one Sep 2026 for your whole firm, shared by every client.
  • A period has no status. It is never open or closed by itself. The statuses on the billing side belong to one billing group’s billing of that period, not to the period. See Billing periods. Locking a bill never locks the work.
  • Fiscal years. For yearly work, the period can follow a client’s fiscal year instead of the calendar year.

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Dates come from periods

Most dates in Flows are counted from a period:
  • 25 days after the period ends
  • on April 15
  • 2 weeks before the period starts
This is why one setup gives the right dates every time. Point the same rule at September and you get September’s dates. Point it at October and you get October’s.
A firm does monthly bookkeeping for Acme and a quarterly review for Beko.
  • Acme’s September bookkeeping points at the month period Sep 2026.
  • Beko’s Q3 review points at the quarter period Q3 2026.
  • When Acme is billed for September, that invoice points at the same Sep 2026.
  • Sep 2026 and Q3 2026 are each one shared period, reused everywhere they apply.
The period a piece of work belongs to and the period you bill it in are set separately, and they’re allowed to differ. See The two clocks.