你的理解完全正确。财年由各个主体自定义，和calendar year不同。calendar year一定是1.1 到12.31

可以这样理解。fiscal year不一定完全是year end ××年12月，准确的fiscal year 可以在公司的年报 审计报告中看到。因为各个公司所处的industry不同，他们的财年划分也会有所不同。比如像迪士尼这类的娱乐游艺类作为主营业务收入的企业，由于78月份假期可能是营业额的峰值，他们可能就会采取以9月为fiscal year end；另外如百货商店这种，年末通常是清仓或者是营业高峰，但是或遇到退货等情况在第二年发生，这样的话事实上fiscal year在第二年的3月这样才能真正反映企业主营业务的财务状况。

假设现在是2016年6月
如果公司的fiscal year end在3月，那么我们现在处于fiscal year 2016，这个财务年对应时间区间为2016.4 - 2017.3；
如果公司的fiscal year end在9月，那么我们现在处于fiscal year 2015，这个财务年对应时间区间为2015.10 - 2016.9。

请问这个解释对吗？

如果不对，那应该如何计算？
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你的例子不對。
1）如果公司的fiscal year end在3月 < --- 現在是六月的話，已經是 fiscal year 2017 （FY2017 是從 2016 年4月一日 到 2017年三月三十一日。)
2）如果公司的fiscal year end在9月<-- 那么我们现在处于fiscal year 2016，这个财务年对应时间区间为2015.10 - 2016.9。

What is the best date for my fiscal year end?
Fiscal year end dates are set using two criteria:

Type of business. A sole proprietorship or a business that is taxed as a sole proprietorship (single-member LLC, for example) must use a December 31 fiscal year-end to match the personal tax year end.


Business cycle. If your business is not taxed as a sole proprietorship, you can choose the end of any quarter for your fiscal year end. Most companies base their fiscal year end of the business cycle for their industry, choosing the end of the busiest time for their fiscal year end.
Companies that do most of their business in the summer might choose a September 30 year end. If your business does a lot of work with the U.S. government, you might choose a September 30 year end to coincide with the federal government's year end. If your business does most of its selling during the holidays, you might choose December 31.

What is a 'Fiscal Year - FY'
A fiscal year (FY) is a period that a company or government uses for accounting purposes and preparing financial statements. A fiscal year may not be the same as a calendar year, and for tax purposes, the Internal Revenue Service (IRS) allows companies to be either calendar-year taxpayers or fiscal-year taxpayers. Fiscal years are commonly referred to when discussing budgets and are often a convenient period to reference when comparing a government's or company's financial performance over time.

BREAKING DOWN 'Fiscal Year - FY'
According to the IRS, a fiscal year consists of 12 consecutive months ending on the last day of any month except December. For example, in terms of tax reporting, a fiscal year may run from Feb. 1 to Jan. 31. Alternatively, instead of observing a 12-month fiscal year, U.S. taxpayers may observe a 52- to 53-week fiscal year, where each year rotates between being 52 or 53 weeks long.
IRS Deadlines for Fiscal-Year Taxpayers
The default IRS system is based on the calendar year, so fiscal-year taxpayers have to make some adjustments to the deadlines for filing certain forms and making certain payments. In particular, while most taxpayers must file by April 15 following the year for which they are filing, fiscal-year taxpayers must file by the 15th day of the fourth month following the end of their fiscal year. To illustrate, a business observing a fiscal year from June 1 to May 31 must submit its tax return by Sept. 15.

Choosing Between Calendar Years and Fiscal Years
In the United States, eligible businesses can adopt a fiscal year for tax reporting purposes simply by submitting their first income tax return observing that fiscal tax year. At any time, these businesses may elect to change to a calendar year. However, businesses that want to change from a calendar year to a fiscal year must get special permission from the IRS or meet one of the criteria outlined on Form 1128, Application to Adopt, Change, or Retain a Tax Year.

How to Refer to a Fiscal Year
Fiscal years are referenced by their end date or end year. For example, the federal government's fiscal year begins on Oct. 1 and ends on Sept. 30. To reference one of the government's fiscal years, a speaker may say, "the fiscal year ending Sept. 30, 2016." Similarly, if a speaker referred to government spending that occurred on Nov. 15, 2015, she would label that as an expenditure for the 2016 fiscal year.