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Tax Due Dates and New Client Checklist

The documents to gather before a first meeting with MangoBooks, and federal and California tax due dates from October 2026 through October 2027.

New Client Document Checklist

Gather the items that apply. Copies and downloaded statements are fine.

Individuals

  • Federal and California returns for the last two or three years.
  • Form W-2 from each employer.
  • Brokerage and bank tax statements, including Forms 1099-B, 1099-DIV and 1099-INT.
  • Form 1099-R for distributions from retirement plans or IRAs.
  • Forms 1099-NEC or 1099-MISC for freelance or contract income.
  • Schedules K-1 from partnerships and S corporations.
  • Form 1098 for mortgage interest, and property tax bills.
  • Receipts for charitable contributions.
  • Records of federal and California estimated tax payments made during the year.
  • The dates of any move into or out of California during the year.

Rental Property Owners

  • For each property, the rent received and the expenses paid, such as repairs, insurance, management fees, utilities and HOA dues.
  • Last year's depreciation schedule.
  • The closing statement for any property bought or sold during the year.
  • Form 593, if California tax was withheld when a property was sold.

Stock Compensation

  • Year-end statements from the brokerage and the stock plan administrator, including any supplemental cost-basis statement.
  • Form 3921 for each ISO exercise and Form 3922 for ESPP shares.
  • Vesting and exercise confirmations for the year.
  • A record of workdays by state, if any work was done outside California while shares were vesting or options were outstanding.

Businesses

  • Articles of organization or incorporation, and the operating agreement or bylaws.
  • The IRS letter assigning the employer identification number and, for an S corporation, the IRS letter accepting the election.
  • Federal and California business returns for the last two or three years, with depreciation schedules.
  • Access to the accounting file, or bank and credit card statements for the year.
  • Loan statements and a list of equipment or other assets bought or sold.
  • Payroll reports, including Forms 941, California Forms DE 9 and DE 9C, and Forms W-2.
  • Forms 1099-NEC issued to contractors.
  • Records of estimated tax payments, and for an LLC, the California annual tax and fee payments made with forms FTB 3522 and FTB 3536.
  • Any change in ownership during the year.

Tax Due Dates

The dates below are for calendar-year filers. When a due date falls on a Saturday, Sunday or legal holiday, it moves to the next business day, and the dates shown already reflect that. The IRS postpones deadlines for areas covered by a disaster declaration, so affected taxpayers may have later dates.

Individuals

  • Thursday, October 15, 2026. Extended 2025 federal and California individual returns are due.
  • Friday, January 15, 2027. Fourth 2026 estimated tax payment, federal and California; the California payment is 30 percent of the year's estimate.
  • Thursday, April 15, 2027. 2026 federal Form 1040 and California Form 540 are due, along with any balance owed. This is also the deadline to request a federal extension on Form 4868; California extends automatically, but payment is still due. First 2027 estimated tax payment, federal and California (30 percent).
  • Tuesday, June 15, 2027. Second 2027 estimated tax payment, federal and California (40 percent).
  • Wednesday, September 15, 2027. Third 2027 federal estimated tax payment. California has no September payment.
  • Friday, October 15, 2027. Extended 2026 federal and California individual returns are due.

Businesses

  • Thursday, October 15, 2026. Extended 2025 federal C corporation returns (Form 1120) are due. Extended 2025 California returns for partnerships (Form 565), and for LLCs classified as partnerships or owned by an individual (Form 568), are due.
  • Monday, November 2, 2026. Last day to file third-quarter federal Form 941 and California Forms DE 9 and DE 9C.
  • Monday, November 16, 2026. Extended 2025 California C corporation returns (Form 100) are due.
  • Tuesday, December 15, 2026. Fourth 2026 estimated tax payment for corporations, federal and California (Form 100-ES).
  • Monday, February 1, 2027. Forms W-2 are due to employees and the Social Security Administration. Forms 1099-NEC are due to recipients and the IRS. Fourth-quarter Form 941 and annual Form 940 are due. Last day to file fourth-quarter California Forms DE 9 and DE 9C.
  • Monday, March 15, 2027. 2026 S corporation returns (federal Form 1120-S and California Form 100S) are due. 2026 partnership returns (federal Form 1065 and California Form 565) and California Form 568 for LLCs classified as partnerships are due. Federal extensions for these returns are requested on Form 7004 by the same date. This is also the last day for an existing calendar-year corporation to file Form 2553 to be an S corporation for 2027.
  • Thursday, April 15, 2027. 2026 C corporation returns (federal Form 1120 and California Form 100) are due. California Form 568 for a single-member LLC owned by an individual is due. The 2027 California LLC annual tax of $800 is due with form FTB 3522. First 2027 estimated tax payment for corporations, federal and California.
  • Friday, April 30, 2027. Last day to file first-quarter federal Form 941 and California Forms DE 9 and DE 9C.
  • Tuesday, June 15, 2027. Second 2027 estimated tax payment for corporations, federal and California. The estimated 2027 California LLC fee is due with form FTB 3536. The first California pass-through entity elective tax payment is due for S corporations and partnerships that plan to elect for 2027.
  • Monday, August 2, 2027. Last day to file second-quarter federal Form 941 and California Forms DE 9 and DE 9C.
  • Wednesday, September 15, 2027. Extended 2026 S corporation returns (federal Form 1120-S and California Form 100S) and extended federal partnership returns (Form 1065) are due. Third 2027 estimated tax payment for corporations, federal and California.
  • Friday, October 15, 2027. Extended 2026 federal C corporation returns (Form 1120) are due. Extended 2026 California returns for partnerships (Form 565), and for LLCs classified as partnerships or owned by an individual (Form 568), are due.
  • Every one or two years. California LLCs file a Statement of Information with the Secretary of State every two years, and corporations every year, by the end of the calendar month in which the company was originally registered.

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