Xbox subscription 36-month limit

Since Sep. 2018, I have gifted Xbox Live Gold, 12 months at a time, to my brother-in-law Aaron (gamertag OnlyRev0lutions), and each time, kept the automatic renewal option turned on for the free 13th month (except once, when the option was not available).

Below are said renewals, in the format:

• renewal date

• renewal method

• interval of dates of next automatic renewal, before & after this renewal

• number of days added, according to TimeAndDate.com’s Days Calculator, excluding end (or start) date from the calculation

• Sep. 15, 2018

• prepaid code, 12 months + 1 month free

• Oct. 1, 2018 - Oct. 31, 2019

• 395 days

• Oct. 12, 2019

• prepaid code, 12 months + 1 month free

• Oct. 31, 2019 - Dec. 1, 2020

• 397 days

• Dec. 1, 2020

• automatic, 12 months (charged to his credit card, reimbursed him cash)

• Dec. 1, 2020 - Dec. 1, 2021

• 365 days

• Dec. 26, 2020

• prepaid code, 12 months + 1 month free

• Dec. 1, 2021 - Jan. 1, 2023

• 396 days

• Feb. 3, 2021

• prepaid code, 12 months + 1 month free

• Jan. 1, 2023 - Jan. 29, 2024

• 393 days

For the last renewal, I waited until February to add the 3rd of 3 years of Gold stacked at once, so that with the free 13th month for keeping auto-renewal on, he would not hit the 36-month limit, and lose any days from the 3rd year - I am now waiting until March to convert it all to Game Pass Ultimate for him (with the regular 1 month for $1, since the current 3-month offer will end before then).

However, after adding the 3rd year of Gold on Feb. 3, 2021, the number of days added seems to be 3 days less than it should have been: based on the 396-day average of the 1st three 13-month renewals above, I calculated that his next renewal date should be Feb. 1 (not Jan. 29), 2024.

I thought Feb. 3 was long enough to wait, based on the following math:

1 month

= 365 days/year ÷ 12 months/year

= 30 5/12 days/month (30.41666...)

x 36 months

= 1,095 days

Or, to account for leap years:

1 month

= (365 x 3 + 366) ÷ 48

= 30.4375 days

x 36 months

= 1,095.75 days

Whether I round down to 1,095, or up to 1,096:

Feb. 1, 2024 (calculated next-renewal date)

- Feb. 3, 2021 (date 3rd year added)

= 1,093 days (36 months minus 2-3 days)

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Therefore, I have a few questions:

• For Xbox subscriptions (Gold, Game Pass, GP Ultimate), 1 month - and by extension, 36 months - is defined as how many days, precisely?

• Did Aaron’s account somehow hit the 36-month limit, anyway?

• If so, until what date in February should I have waited to add the 3rd year of Gold, to keep him under the limit?

• For the 1 month of Ultimate to convert in March, until what date should I wait, to keep him under the limit?

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Sorry if it’s a lot to take in, and thank you for any assistance you can provide.

:)