banking.bacs-processing-date

def bacs_processing_dates(submission_iso: str, after_cutoff: bool) -> BacsCycle

@dataclass(frozen=True)
class BacsCycle:
    """The three days of one Bacs cycle."""

    #: day 1: the file is accepted
    input_day: str
    #: day 2: Bacs processes it and sends it to the receiving banks
    processing_day: str
    #: day 3: the money leaves one account and arrives in the other
    entry_day: str

from fune.banking.bacs_processing_date import bacs_processing_dates  # banking.bacs-processing-date@^1

from typing import List, Sequence

from .banking_bacs_processing_date_types import BacsCycle
from .dates_add_business_days import add_business_days  ← from dates.add-business-days ^1.0.0 · built alongside by fune
from .dates_bank_holidays import bank_holidays  ← from dates.bank-holidays ^1.0.0 · built alongside by fune
from .dates_day_of_week import is_weekday  ← from dates.day-of-week ^1.0.0 · built alongside by fune


def _holidays_for(years: Sequence[int]) -> List[str]:
    out: List[str] = []
    for year in years:
        out.extend(holiday.date for holiday in bank_holidays("england-and-wales", year))
    return out


def _cycle_with(submission_iso: str, after_cutoff: bool, holidays: Sequence[str]) -> BacsCycle:
    processing_day = is_weekday(submission_iso) and submission_iso not in holidays
    input_day = submission_iso if processing_day and not after_cutoff else add_business_days(submission_iso, 1, holidays)
    return BacsCycle(
        input_day=input_day,
        processing_day=add_business_days(input_day, 1, holidays),
        entry_day=add_business_days(input_day, 2, holidays),
    )


def bacs_processing_dates(submission_iso: str, after_cutoff: bool) -> BacsCycle:
    """The Bacs cycle a file joins.

    Bacs works on processing days - Monday to Friday except England and Wales
    bank holidays - and a file joins the cycle whose input day is the day it
    arrives, if that is a processing day and it arrived before the 22:30
    deadline, or the next processing day otherwise. Processing is the next
    processing day and entry the one after.
    """
    if not isinstance(after_cutoff, bool):
        raise TypeError("afterCutoff must be a boolean, received %r" % (after_cutoff,))
    # is_weekday validates the date before its year is read.
    is_weekday(submission_iso)
    year = int(submission_iso[0:4])
    # Only reach for next year's calendar when the cycle really runs into it,
    # so a December submission in the last published year still works as long
    # as its cycle ends inside that year.
    cycle = _cycle_with(submission_iso, after_cutoff, _holidays_for([year]))
    if cycle.entry_day[0:4] != submission_iso[0:4]:
        cycle = _cycle_with(submission_iso, after_cutoff, _holidays_for([year, year + 1]))
    return cycle

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 3 dependencies, pins them in fune.lock, downloads only the Python package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add banking.bacs-processing-date

The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./banking.bacs-processing-date-1.0.0-python.fune, or fetch it from a terminal with fune pull banking.bacs-processing-date@1.0.0:python.

The whole function, every language, is one file too: banking.bacs-processing-date-1.0.0.fune, 16,519 bytes, sha256 d6c142dfcdfc0352df592c4b9d80d19c87383647f6a4e1a3df99f140b852d8cf. It installs into a project of any language.

# fune: before banking.bacs-processing-date

# fune: after banking.bacs-processing-date

# fune: replace dates.add-business-days in banking.bacs-processing-date
# fune: replace dates.bank-holidays in banking.bacs-processing-date
# fune: replace dates.day-of-week in banking.bacs-processing-date

# fune: step banking.bacs-processing-date after <n|label>

More from the author

Bacs describes the cycle for Direct Credit as: "Input day is the latest day a business user/bureau may submit a payment file to Bacs for a processing cycle. Payment files must be transmitted to Bacs between 07.00 and 22.30"; on day 2 files are delivered to the receiving banks; on day 3 "payments are simultaneously credited to the recipients' accounts and debited from your account". Source: Bacs, "Bacs Direct Credit", https://www.bacs.co.uk/bacs-schemes/getting-started/bacs-direct-credit/ (read 2026-09-23).

The days are Bacs processing days: Monday to Friday, excluding bank holidays in England and Wales, which Bacs uses as its non-processing days for the whole of the UK (Scotland's and Northern Ireland's extra holidays do not stop Bacs). The published Bacs processing calendar is the authority; the bank holidays here come from `dates.bank-holidays` (gov.uk data, region `england-and-wales`), and the working-day steps from `dates.add-business-days`.

So:

- input day = the submission date if it is a processing day and the file was sent by 22:30 (`afterCutoff` false); otherwise the next processing day. A file sent at a weekend or on a bank holiday joins the next processing day whatever the time; - processing day = the next processing day after the input day; - entry day = the processing day after that.

## Why `afterCutoff` is a flag

The time of day is the caller's to read (this capability never reads a clock), and comparing a timestamp with 22:30 is simpler at the call site than passing a time zone in. The 22:30 deadline is the one Bacs publishes (quoted above); a bureau or bank may set an earlier internal deadline, in which case pass `afterCutoff` against that.

## Limits

The bank holiday data covers the years gov.uk publishes (2019 to 2028 in `dates.bank-holidays@1.0.0`). A cycle that needs a year outside it fails with that capability's error rather than treating an unknown Christmas as a working day. Next year's calendar is only consulted when the cycle actually runs into next year, so a December cycle in the last published year still works.

This gives the cycle for a submission. It does not work backwards from a required arrival date; for that, step back two processing days from the entry day with `dates.add-business-days` and the same holiday list.

Files