How Australian Financial Year Week Numbers Are Calculated

Australian Financial Year week numbers are computed as floor((date − 1 July) / 7) + 1. Week 1 starts on 1 July of the FY start year. Each subsequent week begins exactly seven days later, on the same weekday as 1 July.

The AU FY anchor: 1 July

The Australian financial year runs from 1 July to 30 June. The Australian Taxation Office defines this boundary; see https://www.ato.gov.au/ for primary guidance.

Week 1 of every AU FY starts on 1 July, whichever weekday that falls on. There is no Monday alignment in this scheme. The anchor is the date, not the weekday.

Step-by-step algorithm

The algorithm has three steps. It works for any date in any AU FY.

Determine the FY start year. If the month is July through December, the FY start year equals the input year. Otherwise the FY start year equals the input year minus 1. Write the financial year as FY<start>-<start+1 mod 100>.
Compute the anchor date: 1 July of the FY start year.
AU FY week number = floor((input date − anchor) / 7 days) + 1.

Every output is an integer between 1 and 53.

Worked examples

Four examples cover the boundary, an early week, a midyear date, and the final week.

1 July 2025 (Tue) gives FY2025-26 week 1.

FY start year is 2025. Anchor is 1 July 2025.
Days since anchor = 0.
Week number: floor(0 / 7) + 1 = 1.

8 July 2025 (Tue) gives FY2025-26 week 2.

FY start year is 2025. Anchor is 1 July 2025.
Days since anchor = 7.
Week number: floor(7 / 7) + 1 = 2.

28 May 2026 (Thu) gives FY2025-26 week 48.

Month is May, so FY start year is 2025. Anchor is 1 July 2025.
Days since anchor = 331.
Week number: floor(331 / 7) + 1 = 47 + 1 = 48.

30 June 2026 (Tue) gives FY2025-26 week 53.

Month is June, so FY start year is 2025. Anchor is 1 July 2025.
Days since anchor = 364.
Week number: floor(364 / 7) + 1 = 52 + 1 = 53.

FY2025-26 has 53 AU FY weeks because 30 June 2026 is exactly 364 days after 1 July 2025.

Why this rule

Week 1 starts on 1 July, so every AU FY week boundary in this scheme is the same weekday as 1 July of that FY. The algorithm stays trivial. There is no Monday lookup and no edge case for early-July dates. The trade-off is that week boundaries do not align to ISO Mondays.

Mapping AU FY weeks to BAS quarters

BAS quarters are calendar-month-bounded and AU FY weeks are 7-day-bounded, so the mapping is approximate.

Q1 (Jul–Sep) — roughly AU FY weeks 1–13.
Q2 (Oct–Dec) — roughly weeks 14–26.
Q3 (Jan–Mar) — roughly weeks 27–39.
Q4 (Apr–Jun) — roughly weeks 40–52 (or 53).

Excel formula

The formula subtracts the FY anchor from the target date, divides by 7, and rounds down — mirroring the calculator's rule exactly.

=INT((TARGET_DATE - DATE(YEAR(TARGET_DATE) + IF(MONTH(TARGET_DATE) < 7, -1, 0), 7, 1)) / 7) + 1

Code (Python)

The Python implementation mirrors the calculator's rule with one helper.

from datetime import date

def au_fy_week(d: date) -> tuple[str, int]:
    fy_start_year = d.year if d.month >= 7 else d.year - 1
    anchor = date(fy_start_year, 7, 1)
    week = (d - anchor).days // 7 + 1
    fy = f"FY{fy_start_year}-{(fy_start_year + 1) % 100:02d}"
    return fy, week

au_fy_week(date(2026, 5, 28))   # ('FY2025-26', 48)
au_fy_week(date(2026, 6, 30))   # ('FY2025-26', 53)
au_fy_week(date(2025, 7, 1))    # ('FY2025-26', 1)

Compared with ISO 8601

ISO 8601 uses Monday-start weeks anchored to the first Thursday of the calendar year. AU FY here uses 1 July as the fixed anchor and shifts week boundaries to whichever weekday 1 July lands on. The two schemes therefore disagree on both the year anchor and the week-start weekday. See How ISO 8601 Week Numbers Are Calculated for the ISO method.

FAQ

What week of the Australian financial year are we in right now? On 28 May 2026, the AU FY week is FY2025-26 week 48. The current FY started on 1 July 2025 and ends on 30 June 2026.

Does the Australian financial year ever have 53 weeks? Yes. FY2025-26 has 53 weeks because 30 June 2026 sits 364 days after 1 July 2025. Any AU FY spanning 365 or 366 days produces a week 53.

Why don't AU FY weeks start on Monday like ISO weeks? The calculator anchors week 1 to the date 1 July, not to a weekday. This keeps the algorithm simple and matches how businesses count weeks into the financial year.