Substantial Presence Test Calculator

residency_calc.py

#!/usr/bin/env python3

# This script calculates the substantial presence test for US tax purposes.
# Example usage: ./residency_calc.py "2025-02-02,2025-03-03;2024-04-04,2024-05-05;2023-06-06,2023-07-07"

import argparse
from dataclasses import dataclass
from datetime import datetime


@dataclass
class TravelDetails:
    entry: datetime
    exit: datetime


def calculate_substantial_presence(travel_details: list[TravelDetails]) -> bool:
    current_year = datetime.now().year

    days_current_year = datetime.now().timetuple().tm_yday
    days_last_year = 365
    days_second_last_year = 365

    for travel in travel_details:
        if travel.exit.year == current_year:
            exit_day = travel.exit if travel.exit < datetime.now() else datetime.now()
            if travel.entry.year == current_year:
                days_current_year_out = (exit_day - travel.entry).days
            else:
                days_current_year_out = (exit_day - datetime(current_year, 1, 1)).days
            days_current_year -= (days_current_year_out - 1)
        elif travel.exit.year == current_year - 1:
            if travel.entry.year == current_year - 1:
                days_last_year_out = (travel.exit - travel.entry).days
            else:
                days_last_year_out = (travel.exit - datetime(current_year - 1, 1
                                                           , 1)).days
            days_last_year -= (days_last_year_out - 1)
        elif travel.exit.year == current_year - 2:
            if travel.entry.year == current_year - 2:
                days_second_last_year_out = (travel.exit - travel.entry).days
            else:
                days_second_last_year_out = (travel.exit - datetime(current_year - 2, 1
                                                                 , 1)).days
            days_second_last_year -= (days_second_last_year_out - 1)

    print(f'Days current year ({current_year}): {days_current_year}')
    print(f'Days last year ({current_year - 1}): {days_last_year}')
    print(f'Days year before last ({current_year - 2}): {days_second_last_year}')
    return days_current_year >= 31 and days_current_year + (days_last_year // 3) + (days_second_last_year // 6) >= 183


def main():
    parser = argparse.ArgumentParser(description='Calculate substantial presence test')
    parser.add_argument('entries', type=str, help='List of entries and exits in the format "YYYY-MM-DD,YYYY-MM-DD;YYYY-MM-DD,YYYY-MM-DD"')
    args = parser.parse_args()

    travel_details = []
    for entry_exit in args.entries.split(';'):
        entry, exit = entry_exit.split(',')
        travel_details.append(TravelDetails(datetime.strptime(entry, '%Y-%m-%d'), datetime.strptime(exit, '%Y-%m-%d')))

    is_resident = calculate_substantial_presence(travel_details)
    print('Resident' if is_resident else 'Non-resident')


if __name__ == '__main__':
    main()