Holy guacamole. There is so much misinformation here in this thread. Go to the OFFICIAL government information, print it off, read it and and keep it in your "border crossing file". Above all remember "it is ALWAYS at the discretion of the border agent as to how long you are granted to stay in the USA on any one trip. Also be cognizant of the "substantial presence test' plus "closer connection to Canada", and if you are spending year after year as many do up to the 182/183 days per year complete this form and keep a copy with you as well for all previous years when crossing the USA border to present as additional proof, coupled with bank statements, proof of residency in Canada such as utility bills, title of property or rental agreement as well as the usual vehicle registration documents/insurance etc.
In over 20 years of crossing the border we haven't had any issues whatsoever, but "one day" we may, so we keep these documents to hand in the RV with us.
Folks we strongly advocate you do your own Due Diligence through the official resources that are what really matter. We personally know of folks that overstayed their time in the USA, by just a few days, and took over 10 years to be given permission to be able to enter again. We are also aware of folks that haven't adhered to the rules and ended up completing forms after forms after forms and hiring accountants etc to be able to gain entry again to the USA for "unpaid taxes" = their is a reciprocal arrangement to avoid double taxation in both countries. Like I said do your own DD through officialdom, no other sources!!!
From their website:
Substantial Presence Test
You will be considered a U.S. resident for tax purposes if you meet the substantial presence test for calendar year 2015. To meet this test, you must be physically present in the United States on at least:
31 days during 2015, and
183 days during the 3-year period that includes 2015, 2014, and 2013, counting:
All the days you were present in 2015, and
1/3 of the days you were present in 2014, and
1/6 of the days you were present in 2013.
Example.
You were physically present in the United States on 120 days in each of the years 2013, 2014, and 2015. To determine if you meet the substantial presence test for 2015, count the full 120 days of presence in 2015, 40 days in 2014 (1/3 of 120), and 20 days in 2013 (1/6 of 120). Because the total for the 3-year period is 180 days, you are not considered a resident under the substantial presence test for 2015.
The term United States includes the following areas.
All 50 states and the District of Columbia.
The territorial waters of the United States.
The seabed and subsoil of those submarine areas that are adjacent to U.S. territorial waters and over which the United States has exclusive rights under international law to explore and exploit natural resources.
The term does not include U.S. possessions and territories or U.S. airspace.
Days of Presence in the United States
You are treated as present in the United States on any day you are physically present in the country at any time during the day. However, there are exceptions to this rule. Do not count the following as days of presence in the United States for the substantial presence test.
Days you commute to work in the United States from a residence in Canada or Mexico if you regularly commute from Canada or Mexico.
Days you are in the United States for less than 24 hours when you are in transit between two places outside the United States.
Days you are in the United States as a crew member of a foreign vessel.
Days you are unable to leave the United States because of a medical condition that arose while you are in the United States.
Days you are an exempt individual.
Closer Connection to a Foreign Country
Even if you meet the substantial presence test, you can be treated as a nonresident alien if you:
Are present in the United States for less than 183 days during the year,
Maintain a tax home in a foreign country during the year, and
Have a closer connection during the year to one foreign country in which you have a tax home than to the United States
Personally we now complete Form 8840 and carry a copy with us each year also:
Form 8840. You must attach a fully completed Form 8840 to your income tax return to claim you have a closer connection to a foreign country or countries.
If You Do Not Have To File A Return, send the form to the Department of the Treasury, Internal Revenue Service Center, Austin, TX 73301-0215, by the due date for filing Form 1040NR or Form 1040NR-EZ. The due date for filing is discussed later in chapter 7.
If you do not timely file Form 8840, you cannot claim a closer connection to a foreign country or countries. This does not apply if you can show by clear and convincing evidence that you took reasonable actions to become aware of the filing requirements and significant steps to comply with those requirements.
It Takes No More Effort To Aim High Than To Aim Low - Reach For The Stars