What are Q1, Q2, Q3 and Q4 in a calendar year?

A calendar year is divided into four equal quarters: Q1 (January–March), Q2 (April–June), Q3 (July–September) and Q4 (October–December). Each quarter has either 90 or 92 days depending on whether the year is a leap year (Q1 gains a day in leap years).

When does each quarter start and end?

Q1 runs 1 Jan – 31 Mar, Q2 runs 1 Apr – 30 Jun, Q3 runs 1 Jul – 30 Sep, and Q4 runs 1 Oct – 31 Dec. These are fixed dates and do not change between years.

How is the UK fiscal quarter different from the calendar quarter?

The UK tax year starts on 6 April, so UK fiscal Q1 covers April–June, Q2 covers July–September, Q3 covers October–December, and Q4 covers January–March. A date in January that is calendar Q1 is therefore UK fiscal Q4.

What is the US federal fiscal year quarter?

The US federal government fiscal year starts on 1 October, making Q1 October–December, Q2 January–March, Q3 April–June, and Q4 July–September. Many US corporations use a different fiscal year, but the federal schedule is the most common reference point.

How do I calculate what quarter a date falls in manually?

Divide the month number by 3 and round up: quarter = ceil(month / 3). For example, May is month 5, and ceil(5 / 3) = ceil(1.67) = 2, so May is Q2. The same formula works for all twelve months.

Is this calculator accurate for leap years?

Yes. The calculator uses the exact UTC date to count days, and it correctly assigns 29 days to February in leap years. A leap year has 366 days total, with Q1 containing 91 days instead of the usual 90.

Quarter of Year Calculator

Planning a project deadline, filing a quarterly tax return, or simply curious which business quarter a date falls in? This quarter of year calculator gives you the answer in one click — and layers on two progress bars, an exact day count, and a side-by-side comparison of calendar, UK fiscal, and US federal fiscal quarters so you never have to mentally juggle multiple year-start conventions again.

How it works

The calculation is pure date arithmetic, performed entirely in your browser without any network requests.

Step 1 — identify the quarter. Given a date, the tool reads the month number (1–12) and applies the formula:

quarter = ceil(month / 3)

That maps January–March to Q1, April–June to Q2, July–September to Q3, and October–December to Q4.

Step 2 — find the quarter boundaries. Each quarter has a fixed start and end: Q1 is 1 Jan – 31 Mar, Q2 is 1 Apr – 30 Jun, Q3 is 1 Jul – 30 Sep, and Q4 is 1 Oct – 31 Dec. The tool constructs those two boundary dates for the same year as the input, then counts days.

Step 3 — compute day-in-quarter and percentage. The day of the quarter is simply (inputDate - quarterStart) / 86400000 + 1 (milliseconds converted to days). The percentage complete is dayOfQuarter / totalDaysInQuarter * 100, rounded to the nearest whole number.

Step 4 — year-to-date progress. The same arithmetic is applied against 1 January of the same year. A leap-year check ((y % 4 == 0 and y % 100 != 0) or y % 400 == 0) determines whether the year has 365 or 366 days.

Step 5 — fiscal-quarter translation. The tool hard-codes two fixed look-up tables: one for the UK fiscal year (starts 6 April) and one for the US federal fiscal year (starts 1 October). Given the calendar month, each table returns the corresponding fiscal quarter number without any network call.

Worked example

Suppose the date is 15 August 2025.

Month = 8, so calendar quarter = ceil(8 / 3) = Q3 (July–September).
Q3 2025 runs 1 Jul 2025 – 30 Sep 2025, a span of 92 days.
Days from 1 July to 15 August = 31 (July) + 15 (August) = 46 days elapsed, so day 46 of 92 in the quarter — 50% through Q3.
Day of year = 31 (Jan) + 28 (Feb, 2025 is not a leap year) + 31 (Mar) + 30 (Apr) + 31 (May) + 30 (Jun) + 31 (Jul) + 15 (Aug) = 227 of 365 — 62% of the year done.
UK fiscal quarter: August falls in the April–June + July–September UK fiscal split, so it is UK fiscal Q2.
US federal fiscal quarter: August falls in the July–September window of the October-starting federal year, so it is US federal fiscal Q4.

Quarter reference table

Quarter	Calendar months	Days (normal year)	Days (leap year)
Q1	January, February, March	90	91
Q2	April, May, June	91	91
Q3	July, August, September	92	92
Q4	October, November, December	92	92

Q3 and Q4 are the longest quarters at 92 days each. Q1 is the shortest at 90 days (91 in a leap year). Q2 sits in the middle at 91 days — always.

Formula note

The core formula quarter = ceil(month / 3) is equivalent to Math.ceil(month / 3) in JavaScript. It is exact for all 12 months and requires no special-casing. Progress percentage is computed as (dayOfQuarter / totalDaysInQuarter) * 100, which gives a value between 1 / totalDays * 100 on the first day and exactly 100 on the last day of the quarter.

All date arithmetic uses UTC to avoid daylight-saving-time edge cases that can shift a local midnight into the previous day in some time zones.