Calculation Methodology

1. Normalization & Chronological State Machine

CitizenCalc implements client-side regex engines to normalize copy-pasted text strings from the official CBP I-94 Portal. The parsing sequence is executed as follows:

• Character Cleansing: Replaces browser clipboard artifacts, non-breaking spaces (\u00a0), and carriage returns with clean standard whitespace.
• Direction Detection: Because CBP portal logs are listed in reverse chronological order (newest first), the parser scans the overall list direction and automatically reverses it to chronological order. Same-day entries use a tie-breaking check (Arrival first, Departure second represents a reverse chronological copy) to orient correctly.
• Index-Preserving Stable Sort: Each event is tagged with its relative position in the text to guarantee a stable sort, preventing browser runtime sort engines from reshuffling same-day exit-then-return boundaries.
• Chronological State Machine: Loops through events in a single pass:
  • Departure Event: If a departure is already open, it is closed immediately as a `MISSING_ARRIVAL` anomaly (0 days absent) to prevent overlap, and a new departure is opened.
  • Arrival Event: If a departure is open, they are paired as a valid trip. If no departure is open, it is closed as a `MISSING_DEPARTURE` anomaly.

2. U.S. Physical Presence Rules & Day Counting

Under 8 CFR § 316.2(a)(4), naturalization applicants must demonstrate physical presence in the United States for a cumulative period of at least half of the statutory period:

• Standard 5-Year Pathway: Requires at least 30 months, translated to exactly 913 days of U.S. presence out of a 1,826-day statutory window (1,827 days if two leap years are spanned).
• Spousal 3-Year Pathway: Requires at least 18 months, translated to exactly 548 days of U.S. presence out of a 1,095-day statutory window (1,096 days if a leap year is spanned).

The Partial-Day Counting Rule

In accordance with the USCIS Policy Manual (Volume 12, Part D, Chapter 5), any part of a day spent inside the United States counts as a day of presence. Therefore:

3. Continuous Residence Boundaries

Continuous residence requires maintaining the U.S. as your primary permanent home or domicile. CitizenCalc audits individual travel segments against the thresholds set under 8 CFR § 316.5(c):

4. 90-Day Early Filing Window

Under INA § 334(a), applicants may submit Form N-400 up to 90 days before completing their continuous residence requirement.

CitizenCalc implements exact calendar boundary math (rather than dividing by 30-day blocks or calendar months) to locate the window. It counts back exactly 90 calendar days from the 3-year or 5-year LPR anniversary date. If the window covers February 29 (leap year), the algorithm accounts for this extra day in its calendar subtraction.

5. Core Assumptions & Limitations

The calculations performed by CitizenCalc rely on several structural parameters and user configurations:

• Data Integrity Assumption: The parser assumes that the inputs provided represent a complete and chronologically ordered set of exits and entries. Gaps in travel records (such as undocumented land crossings) must be manually corrected.
• No Real-time Database Access: CitizenCalc runs 100% locally in your web browser. It does not communicate with the DHS, USCIS, or CBP database systems.
• Exclusion of Non-Mathematical Disqualifications: Meeting the 913-day (or 548-day) physical presence threshold does not guarantee naturalization. USCIS officers evaluate qualitative eligibility requirements such as tax payment history, good moral character, Selective Service registration, and U.S. domicile maintenance, which cannot be measured by date arithmetic.