finance.uk-bank-rate

def uk_bank_rate(on_date: str) -> BankRate

@dataclass(frozen=True)
class BankRate:
    """The rate in force, and the dates it was in force."""

    #: 375 = 3.75%
    basis_points: int
    #: the day it took effect
    valid_from: str
    #: the day before the next change; null while still in force
    valid_to: Optional[str]

from fune.finance.uk_bank_rate import uk_bank_rate  # finance.uk-bank-rate@^1

from .dates_add_days import add_days  ← from dates.add-days ^1.0.0 · built alongside by fune
from .finance_uk_bank_rate_data import BANK_RATE, BANK_RATE_HISTORY  ← this capability’s own data, compiled from data/bank-rate.json into the same file by fune build
from .finance_uk_bank_rate_types import BankRate


def uk_bank_rate(on_date: str) -> BankRate:
    """Bank Rate in force on a date: the latest change on or before it."""
    add_days(on_date, 0)  # validates the date; ISO dates then compare as strings
    for row in BANK_RATE:
        if on_date >= row.valid_from and (row.valid_to is None or on_date <= row.valid_to):
            return BankRate(basis_points=row.basis_points, valid_from=row.valid_from, valid_to=row.valid_to)
    # A history=current build keeps only the rate in force; answering an older
    # date with it would be exactly the wrong answer this data exists to prevent.
    if BANK_RATE_HISTORY != "full" and len(BANK_RATE) > 0:
        earliest = min(r.valid_from for r in BANK_RATE)
        if on_date < earliest:
            raise ValueError(
                "no Bank Rate on %s: this build was installed with history=%s, so it only carries rates from %s. "
                "Reinstall with history=full for older dates." % (on_date, BANK_RATE_HISTORY, earliest)
            )
    raise ValueError("no Bank Rate on %s" % (on_date,))

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 1 dependency, 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 finance.uk-bank-rate

The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./finance.uk-bank-rate-1.0.1-python.fune, or fetch it from a terminal with fune pull finance.uk-bank-rate@1.0.1:python.

The whole function, every language, is one file too: finance.uk-bank-rate-1.0.1.fune, 19,031 bytes, sha256 4b45acdee1dd9262e18c14d1cc635cc6cd8ae0e61583ea93b4e5adba0f9fdeac. It installs into a project of any language.

# fune: before finance.uk-bank-rate

# fune: after finance.uk-bank-rate

# fune: replace dates.add-days in finance.uk-bank-rate

# fune: step finance.uk-bank-rate after <n|label>

More from the author

Source: Bank of England, "Official Bank Rate history", https://www.bankofengland.co.uk/boeapps/database/Bank-Rate.asp, checked on 23 September 2026 (no change in 2026 up to that date). Rates are held in basis points, which every published rate fits exactly (0.1% is 10).

When the rate changes, publish a new version with the new row and the previous row's `validTo` filled in. The data declares its effective dates, so a `history=current` build ships only the rate still in force and refuses an earlier date, explaining why, rather than answering it with today's rate.

## Notices

Contains public sector information licensed under the Open Government Licence v3.0 (https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).

Contains Bank of England data. Reproduction of data in the Database is subject to the terms of the UK Open Government Licence.

1.0.1 adds its attribution notices (NOTICE). The code and the tests are unchanged.

Files