Fixed costs only affect days within their start/end window — adding a cost today doesn't silently reach back into March. Understanding when and why to backdate is the key piece.
01 The lifecycle rule
See Fixed-cost lifecycle dates for the full rule. The short version: a fixed cost is active on a date if start_date ≤ date AND (end_date IS NULL OR end_date ≥ date). Past days that fall outside the window don't subtract the cost.
02 Backfilling past days
If you're adding a fixed cost that should have applied since (say) the start of the year:
- 1Open Fixed Costs
Click + Add fixed cost.
- 2Set the start date to January 1st
Or whatever date the cost actually started.
- 3Save
Every day from that start date subtracts a slice of this cost.
Your past P&Ls will recompute on the next page load — they'll now show the new fixed cost in their slice math.
03 Why we don't auto-backdate
If we auto-backdated every fixed-cost addition, your historical P&Ls would silently change every time you remembered to add a cost. That breaks any reconciliation with your bookkeeper, your tax return, or your own decisions made with the old data. Explicit start dates put you in control.
04 When to backdate fixed costs
Backdate when the cost was genuinely active in the past:
- You forgot to add a cost during signup. Backdate to your account creation date.
- You're onboarding mid-year. Backdate to January 1st so YTD numbers reflect reality.
- A cost has been around longer than nouz has tracked it. Backdate to its real start date.
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