Form 5805-F (2024): Underpayment of Estimated Tax by Farmers and Fishermen Explained

Form 5805-F is a California Franchise Tax Board document used specifically by farmers and fishermen to figure out whether they owe a penalty for underpaying their estimated state income tax. While most taxpayers who miss estimated payment deadlines have to deal with quarterly penalty calculations, California gives farmers and fishermen a different set of rules because their income tends to be seasonal and unpredictable. This form exists to reflect that reality.

What Form 5805-F Actually Covers

If you earn at least two-thirds of your gross income from farming or fishing, California generally lets you avoid the standard four-installment estimated tax schedule that applies to everyone else. Instead, you have the option to pay your entire estimated tax liability in one installment by January 15 of the following year, or simply file your return and pay the full amount owed by March 1. Form 5805-F is where you show the FTB that you qualify for this treatment and, if you didn’t pay on time or paid too little, calculate the penalty that applies.

The form walks through your required annual payment, compares it to what you actually paid, and determines if there’s an underpayment. If there is, it calculates the penalty amount owed based on the number of days the payment was late and the applicable interest rate set by the state.

Who Needs to File It

You need this form if you meet the farming or fishing income threshold and either missed the January 15 single-installment deadline or underpaid what was required. It’s not something every farmer or fisherman in California has to attach to their return — if you paid your full tax liability on time through the single-installment option, or if you filed and paid in full by March 1, there’s typically no penalty to calculate and no need to submit this form at all.

Where it becomes necessary is when a payment was late, partial, or missed entirely. In those cases, the FTB expects you to self-assess the penalty using Form 5805-F rather than waiting for the agency to send a notice. Filing it proactively with your return can prevent confusion later and gives you a clear paper trail showing how the penalty was calculated.

When and How It’s Used

Form 5805-F is filed alongside your California personal income tax return for the tax year in question — in this case, the 2024 tax year, using the version released for 2025 filings. You’ll need your total tax liability, any withholding, and the dates and amounts of any estimated payments you made. The form then walks you through the underpayment calculation step by step, including how to handle situations where you paid late but still within a reasonable window.

Because the form is a fillable AcroForm PDF, you can complete it directly on your computer before printing or attaching it electronically if you’re filing through tax software that supports it. That said, double-check every calculated field manually — automated PDF calculations sometimes don’t update correctly if you go back and edit an earlier entry.

If you’re unsure whether your specific income mix qualifies you as a farmer or fisherman under California’s definition, the instructions packaged with the form spell out the two-thirds gross income test in detail, including how to treat income from related activities.

For taxpayers juggling multiple California-specific forms during filing season, it’s worth getting familiar with related paperwork too. Fiduciaries handling e-file payments, for example, often need Form 8455-FID, while individuals who choose not to e-file their return may need Form 8454 instead. And if your filing situation involves a registered domestic partnership, FTB Publication 737 covers how California treats that income differently from federal rules.

Once you’ve filled out Form 5805-F, attach it to your California return and keep a copy for your records. If the FTB later disagrees with your penalty calculation, having the completed worksheet on hand makes it much easier to resolve the discrepancy without additional back-and-forth.