ExplainersBack periods
Catching up on back periods
Each back period prices at the rate that was in force for that period, with that rate’s own cite and effective date, and the archive holds the result.
Registering in a new state usually means periods behind you as well as ahead. Back periods are a first-class object here rather than a special case: you open them like any other period, enter or import the counts, and the engine prices each one against the rate that was in force for it.
The rate is resolved by period, never by recency
The registry holds a state’s rate as a series of dated windows, and the engine walks them to find the one covering the filing period. A 2019 quarter prices at the 2019 rate with the 2019 citation, and the current rate is not involved. That is also why every January 1 is a window boundary in a state that re-determines its surcharge annually, even in a year the figure did not move: two determination windows are two windows, and merging them would mis-price every back period and every amended return that touches them.
7 of the shipped states carry more than one rate window today:
| State | Windows | Earliest window on record |
|---|---|---|
| CA California | 5 | 2020-01-01 · $0.30 per line per month · 911 surcharge |
| MN Minnesota | 4 | 2024-07-01 · $0.86 per line per month · Combined 911, TAM and TAP fee |
| AL Alabama | 3 | 2013-10-01 · $1.75 per line per month · Statewide 911 charge |
| CT Connecticut | 3 | 2024-07-01 · $0.73 per line per month · Per-line rate — customer with 1 access line; $0.55 per line per month · Per-line rate — customer with 2 access lines; $0.49 per line per month · Per-line rate — customer with 3 access lines; $0.44 per line per month · Per-line rate — customer with 4 to 5 access lines; $0.37 per line per month · Per-line rate — customer with 6 to 10 access lines; $0.29 per line per month · Per-line rate — customer with 11 to 25 access lines; $0.24 per line per month · Per-line rate — customer with 26 to 50 access lines; $0.18 per line per month · Per-line rate — customer with 51 to 99 access lines; $0.15 per line per month · Per-line rate — customer with 100 or more access lines |
| MI Michigan | 3 | 2008-07-01 · $0.19 per counted unit per month · State 9-1-1 charge |
| SD South Dakota | 2 | 2012-07-01 · $1.25 per line per month · 911 emergency surcharge |
| TN Tennessee | 2 | 2017-07-01 · $1.16 per line per month · 911 surcharge |
A period that straddles a boundary is flagged, not guessed
Where a rate changed inside a period — California carries 5 windows, so its history has boundaries in it — the engine does not pick one rate and move on. It reports that two rates apply inside the period, shows both windows with their own citations and the inputs on each side, and marks the period flagged for review so a person decides before it closes. A flag here is a request to look, and it always arrives with the arithmetic behind it.
California · the window in force now
- Rate
- $0.41 per line per month · 911 surcharge; $0.05 per line per month · 988 surcharge
- Effective
- 2026-01-01 → 2026-12-31
- Cite
- Rev. & Tax. Code §41030(a), (f)(1) — annual determination by the Office of Emergency Services
- Form rev.
- the state publishes no revision label
- Retrieved
- Wed, August 12, 2026 · two independent fetches agree
What comes out
The same thing a current period produces: the state’s own form filled, or a filing packet in the state’s own order, each carrying the rate, effective date, citation, form revision, agency, source URL, and retrieval date that priced it. You review it, sign it, and remit it, and the archive freezes the whole computation onto the row.
Which periods are yours to file is your determination. The product opens the periods you tell it to, prices them, and keeps the record.
This page describes what the states publish and what this product does with it. It is not advice, it renders no judgment on any filing, and it makes no determination about which states are yours — that determination is the provider’s. Every state, shipped or named.