How to Fill Out Form N-400: Step-by-Step Guide

What is Form N-400?

Form N-400 is the official application used to apply for U.S. citizenship through naturalization. It is filed with U.S. Citizenship and Immigration Services (USCIS) and is the same form regardless of whether you are applying based on five years of permanent residency, three years of marriage to a U.S. citizen, or qualifying military service.

The current edition (01/20/2025) is 20 pages long and contains 18 parts, though the core applicant sections are Parts 1 through 16. The form collects your biographical information, immigration history, employment and travel records, family details, and responses to questions about your moral character and attachment to the U.S. Constitution.

You can learn more about the N-400 naturalization package and what a complete filing looks like.

Who is eligible to file Form N-400?

Before filling out the form, confirm that you meet the eligibility requirements. USCIS will deny applications that do not meet these criteria, and you will not receive a refund of the filing fee.

Five-year rule (general)

You may apply if you have been a lawful permanent resident (green card holder) for at least five years, have lived in the United States for at least 30 months out of those five years, and have been physically present in the state or USCIS district where you are filing for at least three months. You must be at least 18 years old at the time of filing.

Three-year rule (spouse of U.S. citizen)

If you are married to and living with a U.S. citizen, and your spouse has been a citizen for at least three years, you may apply after just three years as a permanent resident. You must have been physically present in the U.S. for at least 18 months out of those three years and still be living in marital union with your citizen spouse at the time of filing.

Military service

Members of the U.S. armed forces may qualify for naturalization under special provisions. If you have served for one year or more during peacetime, or any period during a designated period of hostilities, different residency and physical presence requirements apply. Active-duty service members can file from anywhere in the world.

Additional requirements (all categories)

Continuous residence in the U.S. from the date of application through naturalization
Ability to read, write, and speak basic English (with exceptions for age and disability)
Knowledge of U.S. government and history (the civics test)
Good moral character
Willingness to take the Oath of Allegiance to the United States

Documents you will need

Before you start filling out the form, gather these documents. You will need the information they contain to answer the questions accurately, and USCIS may request copies as evidence.

Your green card (Form I-551) — you will need your A-Number, USCIS Online Account Number (if you have one), and the date you became a permanent resident
Travel records — dates of every trip outside the United States during the statutory period (five or three years)
Employment history — employer names, addresses, and dates for the past five years
Residential history — every address where you have lived during the past five years
Marriage certificate (if applying under the three-year rule)
Spouse's proof of U.S. citizenship (if applying under the three-year rule)
Divorce decrees or death certificates for any prior marriages
Court records for any arrests, citations, or criminal charges, even if they were dismissed
Tax returns for the past five years (or three years if applying under the spouse rule)
Two passport-style photographs (2" x 2") — check current USCIS photo requirements

For a printable version of this list tailored to your situation, see our N-400 filing checklist guide.

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FormSnake walks you through every question in plain language, validates your answers in real time, and generates a complete filing package — form, cover letter, checklist, and mailing instructions — as a single PDF.

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Step-by-step walkthrough: Parts 1 through 16

The N-400 is divided into parts. Here is what each one asks for and what you need to know.

Part 1 — Information About Your Eligibility

This section asks you to select the basis for your eligibility. The most common options are: (A) you have been a permanent resident for at least five years, or (B) you have been married to and living with a U.S. citizen for the last three years. Choose the option that applies to you. If you qualify under more than one category, choose the one with the shorter residency requirement.

Part 2 — Information About You

This is the largest section. It collects your full legal name, any other names you have used, date of birth, country of birth, A-Number, Social Security number, and contact information. It also asks about your immigration status, date of admission as a permanent resident, and whether you have ever applied for naturalization before. Answer every field exactly as it appears on your green card and other official documents. Inconsistencies between your N-400 and your immigration records are one of the most common causes of delays.

Part 3 — Accommodations for Disabilities and/or Impairments

If you have a physical or developmental disability or mental impairment, you can request accommodations for your naturalization interview and ceremonies. This includes sign language interpreters, wheelchair accessibility, or modifications to the testing requirements. If you need an exemption from the English or civics requirement due to a disability, you must also file Form N-648 (Medical Certification for Disability Exceptions).

Part 4 — Information About Your Residence

List every address where you have lived during the past five years (or three years if applying under the spouse rule), starting with your current address. Include the dates you lived at each address. USCIS uses this to determine which field office has jurisdiction over your case, so accuracy matters.

Part 5 — Information About Your Parents

Provide your parents' full legal names, dates of birth, countries of birth, and current citizenship status. If either parent is a U.S. citizen, note the date they became a citizen. This information helps USCIS verify whether you may have derived or acquired citizenship through a parent — if so, you may already be a citizen and would need a different process (Form N-600) instead.

Part 6 — Information About Your Marital History

Provide details about your current marriage (if applicable), including your spouse's name, date of birth, citizenship, immigration status, and date and place of marriage. If you have been married before, you must list each prior spouse and explain how each marriage ended (divorce, annulment, or death of spouse). If you are applying under the three-year spouse rule, your current spouse's information is closely scrutinized.

Part 7 — Information About Your Children

List all of your children, regardless of age, marital status, or where they live. Include biological, adopted, and stepchildren. For each child, provide their full name, date of birth, A-Number (if applicable), country of birth, and current address. Missing a child from this list can create serious issues at your interview.

Part 8 — Information About Your Employment and Schools

List every employer and school you have attended during the past five years. For each entry, provide the name, address, your occupation or field of study, and the dates. Gaps in employment are acceptable — just be honest. If you were unemployed, list that as well. USCIS is looking for consistency with your tax records and residency history.

Part 9 — Time Outside the United States

List every trip you took outside the United States during the statutory period. For each trip, provide the date you left, the date you returned, the countries you visited, and the total number of days. This section is critical: any single trip of six months or more may break your continuous residence and require you to restart the clock. Trips of one year or more generally disqualify you unless you obtained a re-entry permit (Form I-131) before departing. Be thorough — check passport stamps and travel records carefully.

Part 10 — Additional Questions: Moral Character and Attachments

This is the longest section and contains approximately 50 yes/no questions. It covers: claims to U.S. citizenship, voting history, tax obligations, affiliations with organizations, military service, criminal history (including arrests that did not lead to conviction), immigration violations, and willingness to take the Oath of Allegiance. Answer every question honestly. USCIS has access to extensive databases and will verify your answers. A "yes" answer does not automatically disqualify you, but a dishonest "no" that USCIS discovers later can result in denial or even revocation of citizenship.

Part 11 — Your Signature

Sign and date the form. Your signature certifies that everything in the application is true and correct to the best of your knowledge. Do not sign until you are ready to mail the form. If you used a preparer or interpreter, they must also sign in the appropriate sections (Parts 12-15).

Parts 12-16 — Preparer, Interpreter, and USCIS Use

Parts 12 and 13 are for your interpreter and preparer (if you used one). Part 14 provides additional space for answers that did not fit in their designated sections. Parts 15 and 16 are for use at the naturalization interview and oath ceremony — USCIS completes these, not you. Leave Parts 15 and 16 blank when filing.

Common mistakes to avoid

USCIS may reject your application outright if the form is incomplete or contains certain errors. Here are the most frequent mistakes applicants make:

Inconsistent names.Your name on the N-400 must match your green card exactly. If your name has changed since your green card was issued, use the name on the card in Part 2 and list your current legal name as an "other name."
Missing travel records. Many applicants forget short trips. USCIS may have records of your border crossings even if you do not. Check passport stamps and airline records before filling out Part 9.
Leaving fields blank.If a question does not apply to you, write "N/A" or "None" rather than leaving it empty. Blank fields can trigger a Request for Evidence (RFE) or cause USCIS to return your application.
Wrong filing fee. The paper filing fee is $760 for all applicants. If you send the wrong amount, your application will be rejected. Check the current fee schedule on uscis.gov before mailing.
Forgetting to sign. An unsigned form will be returned without processing. Sign in ink after reviewing everything.
Wrong mailing address. USCIS has different lockbox addresses depending on where you live and your filing basis. Sending your application to the wrong address can add weeks of delay or result in rejection.
Not disclosing arrests.You must disclose every arrest, charge, and citation — even if it was dismissed, expunged, or sealed. The question asks if you were "ever arrested," not if you were convicted.
Filing too early. You can file up to 90 days before you meet the residency requirement. Filing earlier than that will result in denial.

Where to mail your application

USCIS uses lockbox facilities to receive N-400 applications. The correct lockbox address depends on two factors: which state you live in and whether you are filing based on general eligibility or the three-year spouse rule. There are separate addresses for USPS and courier delivery (UPS, FedEx, DHL).

Check the USCIS N-400 filing page for the current list of lockbox addresses. The addresses change periodically, so always verify before mailing.

When you use FormSnake to prepare your N-400, your filing instructions include the correct lockbox address based on your state and eligibility category — so you do not need to look it up yourself.

What happens after you file

Once USCIS receives your application, the process follows a standard sequence:

Receipt notice (Form I-797C). You will receive a receipt notice confirming that USCIS accepted your application. This typically arrives within two to three weeks of filing. If you included Form G-1145, you will also receive email and text confirmation. Your receipt number lets you track your case online.
Biometrics appointment. USCIS will schedule you for a biometrics appointment at a local Application Support Center (ASC). They will collect your fingerprints, photograph, and signature for background checks. Bring your appointment notice and your green card.
Interview. You will be scheduled for an in-person interview at your local USCIS field office. The officer will review your application, verify your identity, test your English ability, and administer the civics test (you must correctly answer 6 out of 10 questions from the official list of 100). Bring your green card, passport, appointment notice, and any documents that support your application.
Decision. In many cases, the officer will inform you of the decision at the end of your interview. The result will be one of: approved, continued (additional evidence or a retest needed), or denied. If approved, you will be scheduled for an oath ceremony.
Oath ceremony. You will take the Oath of Allegiance at a naturalization ceremony. You will surrender your green card and receive your Certificate of Naturalization (Form N-550). You are a U.S. citizen from the moment you take the oath.

Processing times vary significantly by field office and application volume. Check uscis.gov for current processing times for your specific field office.

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