finance.aged-debt
Aged debt report: open invoices bucketed as current, 1-30, 31-60, 61-90 and 90+ days overdue as at a date.
1.0.0 · published 2026-10-03 by charlie · Anterra
Pinned by 13 tests, run in TypeScript, Python and Rust.
What it does
The aged debtors (or aged creditors) report: what is owed, split by how long it has been overdue as at a date.
Age is counted from the **due date**, not the invoice date, because that is what "overdue" means and what credit control chases. Days overdue is the calendar days from the due date to the as-at date: an invoice due on the as-at date is 0 days overdue and still current; one due the day before is 1 day overdue.
For example
aged_debt(invoices ×8, 2026-06-30, 30, 60, 90, GBP)→ as at 2026-06-30, buckets ×5, total £1,216.00 a ledger across every bucket, each boundary on its edge, with a creditaged_debt(, 2026-06-30, 30, 60, 90, EUR)→ as at 2026-06-30, buckets ×5, total €0.00 an empty ledger still has every bucket, in the given currencyaged_debt(invoices ×1, 2024-03-31, 30, 60, 90, GBP)→ as at 2024-03-31, buckets ×5, total £10.00 leap year: due 31 December 2023 is 91 days overdue on 31 March 2024
The function
The same function in TypeScript, Python and Rust, pinned by the same tests. Pick your language; the choice follows you around the registry.
def aged_debt(invoices: Sequence[OpenInvoice], as_at: str, bucket_days: Sequence[int], currency: str) -> AgedDebt
| invoices | OpenInvoice[] | open items; what is still owed on each |
| as_at | date | the date the report is drawn up to |
| bucket_days | int[] | upper bounds of the overdue buckets, ascending: [30, 60, 90] gives 1-30, 31-60, 61-90 and 90+ |
| currency | string | the report's currency, so an empty ledger still has one |
| returns | AgedDebt |
The types it declares, generated into your project
@dataclass(frozen=True)
class OpenInvoice:
"""One open item on a customer's account."""
reference: str
due_date: str
#: what is still owed; negative for an unallocated credit
outstanding: Money
@dataclass(frozen=True)
class AgedDebtBucket:
"""One column of the report."""
#: "current", "1-30", ... "90+"
label: str
#: fewest days overdue in the bucket; null for current
from_days: Optional[int]
#: most days overdue in the bucket; null for the last
to_days: Optional[int]
total: Money
#: the invoices in the bucket, in input order
references: List[str]
@dataclass(frozen=True)
class AgedDebt:
as_at: str
#: current first, then oldest last
buckets: List[AgedDebtBucket]
#: the sum of every bucket
total: Money
Your code names it in one line, in the file that uses it
from fune.finance.aged_debt import aged_debt # finance.aged-debt@^1
Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.
from typing import List, Optional, Sequence
from .dates_days_between import days_between ← from dates.days-between ^1.0.0 · built alongside by fune
from .finance_aged_debt_types import AgedDebt, AgedDebtBucket, OpenInvoice
from .money_add import add_money ← from money.add ^1.0.0 · built alongside by fune
from .money_amount import Money, money ← from money.amount ^1.0.0 · built alongside by fune
def aged_debt(invoices: Sequence[OpenInvoice], as_at: str, bucket_days: Sequence[int], currency: str) -> AgedDebt:
"""Bucket open invoices by how many days past their due date they are.
Age runs from the due date, not the invoice date: an invoice due today is
current. Every bucket is returned, empty or not, so a report's columns are
fixed.
"""
if len(bucket_days) == 0:
raise ValueError("bucketDays needs at least one boundary")
previous = 0
for bound in bucket_days:
if isinstance(bound, bool) or not isinstance(bound, int) or bound <= previous:
raise ValueError(
"bucketDays must be whole days, ascending, from 1: received %s after %s" % (bound, previous)
)
previous = bound
zero = money(0, currency)
labels: List[str] = ["current"]
froms: List[Optional[int]] = [None]
tos: List[Optional[int]] = [0]
start = 1
for bound in bucket_days:
labels.append("%d-%d" % (start, bound))
froms.append(start)
tos.append(bound)
start = bound + 1
labels.append("%d+" % (start - 1,))
froms.append(start)
tos.append(None)
totals: List[Money] = [zero for _ in labels]
refs: List[List[str]] = [[] for _ in labels]
total = zero
for invoice in invoices:
overdue = days_between(invoice.due_date, as_at)
index = 0
if overdue > 0:
index = len(bucket_days) + 1
for i, bound in enumerate(bucket_days):
if overdue <= bound:
index = i + 1
break
totals[index] = add_money(totals[index], invoice.outstanding)
refs[index].append(invoice.reference)
total = add_money(total, invoice.outstanding)
buckets = [
AgedDebtBucket(label=labels[i], from_days=froms[i], to_days=tos[i], total=totals[i], references=refs[i])
for i in range(len(labels))
]
return AgedDebt(as_at=as_at, buckets=buckets, total=total)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 finance.aged-debt
The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./finance.aged-debt-1.0.0-python.fune, or fetch it from a terminal with fune pull finance.aged-debt@1.0.0:python.
The whole function, every language, is one file too: finance.aged-debt-1.0.0.fune, 22,899 bytes, sha256 c77e4bbac85a53d83b8987eb63d884d81d70c48171fdcd18c47f2fde788d57d0. It installs into a project of any language.
Customise it in your app
The seams this capability offers. Put a marker directly above a function of your own and fune build wires it into the built code; the package on the registry is not changed, the built file’s header lists it under CUSTOMISED, and fune hooks lists every hook in the project. How hooks work.
before — your function gets the arguments and returns them, changed or not, or throws to refuse the call.
# fune: before finance.aged-debt
after — your function gets the result and the arguments, and returns the final result.
# fune: after finance.aged-debt
replace — inside this capability’s code only, calls to a dependency go to your function, with the same signature. Other capabilities that use it are unaffected; write in * to replace it everywhere.
# fune: replace dates.days-between in finance.aged-debt
# fune: replace money.add in finance.aged-debt
# fune: replace money.amount in finance.aged-debt
step — your function runs at a numbered point inside the function’s body, receives the in-scope values it names as parameters, and may return replacements. List the points with fune show finance.aged-debt --steps.
# fune: step finance.aged-debt after <n|label>
Tests
A version published now needs at least 8 tests for every function, and one that expects the error for each function that throws; the registry refuses it otherwise. fune verify --all runs each case in TypeScript, Python and Rust, and a project runs them again with fune verify. This page lists the cases; it does not run them. The exact JSON is vectors.json.
| Case | Arguments | Expected | |
|---|---|---|---|
| a ledger across every bucket, each boundary on its edge, with a credit | invoices ×8, 2026-06-30, 30, 60, 90, GBP | → | as at 2026-06-30, buckets ×5, total £1,216.00 |
| an empty ledger still has every bucket, in the given currency | , 2026-06-30, 30, 60, 90, EUR | → | as at 2026-06-30, buckets ×5, total €0.00 |
| leap year: due 31 December 2023 is 91 days overdue on 31 March 2024 | invoices ×1, 2024-03-31, 30, 60, 90, GBP | → | as at 2024-03-31, buckets ×5, total £10.00 |
| the same invoice a non-leap year later is 90 days overdue, still 61-90 | invoices ×1, 2026-03-31, 30, 60, 90, GBP | → | as at 2026-03-31, buckets ×5, total £10.00 |
| weekly buckets | invoices ×4, 2026-06-30, 7, 14, GBP | → | as at 2026-06-30, buckets ×4, total £10.00 |
| a single boundary | invoices ×2, 2026-06-30, 30, GBP | → | as at 2026-06-30, buckets ×3, total £1.50 |
| invoices due in the future are current | invoices ×1, 2026-06-30, 30, 60, 90, GBP | → | as at 2026-06-30, buckets ×5, total £9.99 |
| no boundaries is refused | , 2026-06-30, , GBP | → | error: bucketDays needs at least one boundary |
| a zero boundary is refused | , 2026-06-30, 0, 30, GBP | → | error: bucketDays must be whole days, ascending, from 1 |
| repeated boundaries are refused | , 2026-06-30, 30, 30, GBP | → | error: bucketDays must be whole days, ascending, from 1 |
Show the other 3 tests
| Case | Arguments | Expected | |
|---|---|---|---|
| descending boundaries are refused | , 2026-06-30, 60, 30, GBP | → | error: bucketDays must be whole days, ascending, from 1 |
| an invoice in another currency is refused | invoices ×1, 2026-06-30, 30, 60, 90, GBP | → | error: currency mismatch |
| an impossible due date is refused | invoices ×1, 2026-06-30, 30, 60, 90, GBP | → | error: not a real calendar date |
More from the author
The buckets are an argument. `[30, 60, 90]` gives the usual report:
| label | days overdue | |---|---| | current | 0 or fewer (not yet due, or due today) | | 1-30 | 1 to 30 | | 31-60 | 31 to 60 | | 61-90 | 61 to 90 | | 90+ | 91 or more |
`[7, 14]` gives current, 1-7, 8-14 and 14+. The bounds must be whole days, ascending, the first at least 1. The last label reads "90+" as reports print it, and `fromDays` (91) says exactly where it starts.
Every bucket appears, even when empty, so the columns of a report never move. Each lists the references it holds in input order, so a total can always be traced to its invoices. An unallocated credit (a negative outstanding amount) reduces the bucket it falls in, as it does on a statement; allocating credits to invoices first is the caller's choice.
Calendar days, not 30-day months: an invoice due on 31 December 2023 is 91 days overdue on 31 March 2024 (a leap year) but 90 days overdue on 31 March 2026, so it is "90+" in one report and "61-90" in the other.
Files
| Path | Bytes |
|---|---|
| README.md | 1,457 |
| impl/python.py | 2,252 |
| impl/rust.rs | 4,122 |
| impl/typescript.ts | 2,211 |
| vectors.json | 7,733 |