retail.oss-vat

def oss_vat(net: Money, seller_country: str, customer_country: str, eu_sales_previous_year: Money, eu_sales_this_year: Money, opted_in: bool, on_date: str) -> OssVat

@dataclass(frozen=True)
class OssVat:
    """Where VAT is due, at what rate, and how much."""

    #: the member state whose VAT applies
    tax_country: str
    #: domestic (same country), origin (below the threshold: the seller's own VAT) or oss (the customer's VAT, declared through the One Stop Shop)
    scheme: str
    #: that state's standard rate
    basis_points: int
    #: the EUR 10,000 threshold is exceeded this year or was last year
    threshold_exceeded: bool
    net: Money
    #: net at the rate, rounded half up
    vat: Money
    gross: Money

from fune.retail.oss_vat import oss_vat  # retail.oss-vat@^1

import re

from .money_amount import Money, money  ← from money.amount ^1.0.0 · built alongside by fune
from .money_apply_rate import apply_rate  ← from money.apply-rate ^1.0.0 · built alongside by fune
from .retail_oss_vat_data import OSS_RULES, OSS_RULES_HISTORY  ← this capability’s own data, compiled from data/oss-rules.json into the same file by fune build
from .retail_oss_vat_types import OssVat

_ISO_DATE = re.compile(r"^\d{4}-\d{2}-\d{2}$")
_COUNTRY = re.compile(r"^[A-Z]{2}$")


def _country(code: str, name: str) -> str:
    # The EU writes Greece as EL in VAT matters; ISO 3166 says GR. Accept both.
    if not isinstance(code, str) or not _COUNTRY.match(code):
        raise ValueError('%s must be an ISO 3166-1 alpha-2 code, received "%s"' % (name, code))
    return "GR" if code == "EL" else code


def _is_member(code: str) -> bool:
    return any(r.rule == "standard-rate" and r.country == code for r in OSS_RULES)


def _lookup(rule: str, where: str, on_date: str) -> int:
    best = None
    for r in OSS_RULES:
        if r.rule != rule or r.country != where:
            continue
        if on_date < r.valid_from or (r.valid_to is not None and on_date > r.valid_to):
            continue
        if best is None or r.valid_from > best.valid_from:
            best = r
    if best is not None:
        return best.value
    # A history=current build carries only the rules still in force; answering
    # an older date with today's rate is the failure the dates exist to prevent.
    if OSS_RULES_HISTORY != "full":
        earliest = None
        for r in OSS_RULES:
            if r.rule == rule and r.country == where and (earliest is None or r.valid_from < earliest):
                earliest = r.valid_from
        if earliest is not None and on_date < earliest:
            raise ValueError(
                'no OSS rule "%s" for %s on %s: this build was installed with history=%s, '
                "so it only carries rules from %s. Reinstall with history=full for older supplies."
                % (rule, where, on_date, OSS_RULES_HISTORY, earliest)
            )
    raise ValueError('no OSS rule "%s" for %s on %s' % (rule, where, on_date))


def oss_vat(
    net: Money,
    seller_country: str,
    customer_country: str,
    eu_sales_previous_year: Money,
    eu_sales_this_year: Money,
    opted_in: bool,
    on_date: str,
) -> OssVat:
    """VAT on a business-to-consumer sale to another EU member state: the
    seller's own rate while its cross-border sales stay within EUR 10,000 (and
    it has not opted in), the customer's state's rate through the One Stop Shop
    once they exceed it, and always the customer's for sellers outside the EU.
    """
    if not isinstance(on_date, str) or not _ISO_DATE.match(on_date):
        raise ValueError('onDate must be an ISO date (YYYY-MM-DD), received "%s"' % (on_date,))
    seller = _country(seller_country, "sellerCountry")
    customer = _country(customer_country, "customerCountry")
    if not _is_member(customer):
        raise ValueError('customer country "%s" is not an EU member state' % customer_country)
    for name, amount in (("euSalesPreviousYear", eu_sales_previous_year), ("euSalesThisYear", eu_sales_this_year)):
        if amount.currency != "EUR":
            raise ValueError("%s must be in EUR, received %s" % (name, amount.currency))
        if amount.minor < 0:
            raise ValueError("%s must not be negative, received %d" % (name, amount.minor))

    threshold = _lookup("distance-selling-threshold", "EU", on_date)
    threshold_exceeded = eu_sales_previous_year.minor > threshold or eu_sales_this_year.minor > threshold

    if seller == customer:
        scheme, tax_country = "domestic", customer
    elif _is_member(seller) and not threshold_exceeded and not opted_in:
        scheme, tax_country = "origin", seller
    else:
        scheme, tax_country = "oss", customer

    basis_points = _lookup("standard-rate", tax_country, on_date)
    vat = apply_rate(net, basis_points, "half-up")
    return OssVat(
        tax_country=tax_country,
        scheme=scheme,
        basis_points=basis_points,
        threshold_exceeded=threshold_exceeded,
        net=net,
        vat=vat,
        gross=money(net.minor + vat.minor, net.currency),
    )

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 2 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 retail.oss-vat

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

The whole function, every language, is one file too: retail.oss-vat-1.0.0.fune, 41,812 bytes, sha256 0db7e57e14bedd5cedc92cb6317fd07a407ca6cd0fed2c85e45e79a207e3849a. It installs into a project of any language.

# fune: before retail.oss-vat

# fune: after retail.oss-vat

# fune: replace money.amount in retail.oss-vat
# fune: replace money.apply-rate in retail.oss-vat

# fune: step retail.oss-vat after <n|label>

More from the author

- **Same country** as the seller: a domestic sale at that country's rate (`domestic`). - **Seller established in one EU member state, small:** while its total cross-border B2C distance sales and TBE services to other member states stay at or below EUR 10,000 in the current calendar year, and did in the previous one, it charges its own country's VAT (`origin`). The sale that takes this year's total over EUR 10,000 is already taxed at destination, which is why `euSalesThisYear` includes this supply. A seller may opt to tax at destination anyway (`optedIn`); the option binds for two calendar years. - **Otherwise**, and always for sellers established outside the EU: the customer's member state's VAT (`oss`).

VAT is `net x rate`, rounded half up to the minor unit with `money.apply-rate`. A negative net (a credit note) gives negative VAT.

## Rates are dated data

`data/oss-rules.json` holds each member state's **standard** rate from the start of OSS on 2021-07-01, with each change since on its effective date, and the EUR 10,000 threshold (in euro cents) as a dated row too. Rows that say 2021-07-01 are rates that were already in force then, not their enactment dates. Changes recorded: Luxembourg 17% to 16% for 2023 and back to 17% from 2024; Estonia 20% to 22% from 2024-01-01 and 24% from 2025-07-01; Finland 24% to 25.5% from 2024-09-01; Slovakia 20% to 23% from 2025-01-01; Romania 19% to 21% from 2025-08-01.

A build installed with `history=current` keeps only the rates in force and refuses an older date rather than answering it at today's rate.

## Not modelled

- Reduced, super-reduced and parking rates. Books, food, children's clothes and much else are taxed at reduced rates that differ by country and product; this capability knows only standard rates, so a caller selling reduced-rate goods must look the rate up by product. - Territories outside the EU VAT area (the Canary Islands, whose 7% "VAT" row appears in the Commission's database, Åland, Mount Athos and others) and the reduced rates of Madeira and the Azores. - Imports in consignments up to EUR 150 (the Import One Stop Shop, IOSS), Northern Ireland sellers (XI), and deemed-supplier rules for marketplaces. - Converting sales totals into euros: pass the thresholds in EUR, converted as the member state of identification requires.

## Sources

- Standard rates: European Commission, Taxes in Europe Database (TEDB), queried through its VAT retrieval service (https://ec.europa.eu/taxation_customs/tedb/ws/, WSDL VatRetrievalService.wsdl) on 2026-09-23 for all 27 member states, from 2021-07-01 to 2026-09-23. Human-readable entry point: https://taxation-customs.ec.europa.eu/taxation/vat/vat-directive/vat-rates_en (links to TEDB, https://ec.europa.eu/taxation_customs/tedb/). The database returned semi-annual snapshots; the change dates above are the effective dates of the national measures, each confirmed by the snapshots either side. The latest snapshot the service returned is 2026-07-01 for most states, 2026-01-01 for Cyprus and Portugal and 2025-01-01 for Greece; their rates are assumed unchanged since, and should be re-checked before publishing. - Threshold: Council Directive 2006/112/EC (the VAT Directive), article 59c, as amended by Council Directive (EU) 2017/2455; the application date was moved to 1 July 2021 by Council Decision (EU) 2020/1109. The Commission's "Guide to the VAT One Stop Shop" (section on the EUR 10 000 threshold) states the rule used here: one threshold for TBE services and intra-EU distance sales together, net of VAT, current and preceding calendar year, for suppliers established in only one member state: https://vat-one-stop-shop.ec.europa.eu/system/files/2021-07/OSS_guidelines_en.pdf and the list of legal acts at https://vat-one-stop-shop.ec.europa.eu/vat-e-commerce/eu-legislation_en

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