# Calling window

A calling window is the span of local hours a sender contacts people in. Spaw answers in_call_window from the number's time zones: clock arithmetic, not compliance advice.

Date: 2026-09-27

A calling window is the span of local hours in which a sender is prepared to call or text someone, such as 09:00 to 20:00 at the recipient's end. Spaw checks a window against the time zones of the number, which are the zones where it was issued and not always where the person is.

## What Spaw answers

Every answer carries `utc_offsets`, the distinct current UTC offsets across the number's `timezones`, sorted west to east, and `local_time`, the local time now, when every one of those zones shares a single offset. Send `call_window` as two 24-hour local times, `"09:00-20:00"`, with a single lookup or a batch and the answer carries `in_call_window`: true when the local time in every zone is inside the window, false when any is outside. The window runs from its start up to, not including, its end, may run past midnight (`"21:00-08:00"`), and is empty when start and end are equal, which always answers false. `in_call_window` is null without a window, when the number has no zone (an [international network number](/glossary/international-network-number) has none), and on an answer served from the suppression list; bulk runs take no window. Nothing is stored: the clock is worked out on every request.

Most numbers have one zone, but not all. When the example mobile number of each region in libphonenumber 9.0.37 was looked up on 27 September 2026, 15 of the 244 answered more than one zone: the Russian one thirteen, the Australian one six. There `local_time` is null whenever the zones disagree, and a window has to hold in all of them at once. `in_call_window` is not one of the [SMS policy](/glossary/sms-policy)'s rules, so it never changes `ok_to_send`.

## What it does not mean

The zone is where the number was issued, not where the person is: a mobile travels with its owner, a VoIP number can be answered anywhere, and a ported number keeps the zones of its code. `in_call_window` is clock arithmetic, not compliance advice. The US rule, for example, counts the hours at the called party's location: it bars telephone solicitation of a residential subscriber "before the hour of 8 a.m. or after 9 p.m. (local time at the called party's location)" (47 CFR 64.1200(c)(1), https://www.law.cornell.edu/cfr/text/47/64.1200, accessed 27 September 2026). No holiday calendar or do-not-call register is checked. You choose the window. Whether a country keeps one clock or several is on its page under [phone facts by country](/tools/phone-number-lookup/countries).

Reference: https://spaw.co/glossary/calling-window