Official sources on the timeline seem to be self-contradictory. Mokuba Kaiba's recollection of Seto Kaiba's past means Seto would be 16 at the time of Death-T. However Seto's age at the time of graduation, birthday and the timing of Death-T indicate he should be 15. If you have any insights, please discuss on the talk page.
Events from the Yu-Gi-Oh! manga are considered to have taken place in the timelines for R, GX and The Dark Side of Dimensions. However events from R, GX and The Dark Side of Dimensions do not necessarily take place within each others' timelines.
↑"1960" is mentioned at the beginning of the chapter. Sugoroku is 43 at the time and is 72 sometime between April 1996 and September 1997, suggesting 1960 is the decade rather than the year.
↑Keith was 26, during Duelist Kingdom, which seems to have taken place in 1997, before his birthday
↑Rishid is 25, during Battle City, which seems to take place in 1997, before his birthday. He also mentions being born about 5 years before Ishizu and 9 years before Marik.
↑Pegasus is 24 during Duelist Kingdom, which seems to take place in spring 1997, placing 1972 as his birth year.
↑Mai and Pegasus were 24 at the same time when they appeared. Neither of their birthdays had passed the year when they both appeared, suggesting they were born the same year.
↑Ishizu was 20 during Battle City, which seems to take place sometime between mid-April and September, suggesting 1977 is her birth year.
↑Jonouchi was born January 25 and was 16 in summer 1996, meaning he was born in 1980. Although, this would mean he started high school at 16, rather than the usual 15.
↑Esper was 17 during Battle City, which took place in 1997, after his birthday.
↑Yugi was born June 4 and was 18 in March 1999, implying 1980 is his birth year.
↑Kaiba was born October 25 and was 18 in March 1999, implying 1980 is his birth year.
↑Marik is 16 during Battle City, which seems to takes place between April and September 1997, suggesting 1980 is his birth year. Rishid said Marik was born 4 years after Ishizu. This may have been a rounding up from 3 years and 8 months.
↑This event took place while Seto was ten years old. Given he was born October 25, 1980, the event took place between October 25, 1990 and October 24, 1991
↑Seto and Mokuba were put in an orphanage shortly after their father's death.
↑Seto and Mokuba were adopted not long after being put in the orphanage and six years before Gozaburo's death.
↑Duelist Kingdom seems to have taken place in spring 1997. Jonouchi said that his parents separated six years earlier. Given he may have rounded a few months, the separation seems to have occurred in late 1990 or 1991.
↑This took place one year after Marik's Rite of the Tomb Guardians and five years before Battle City.
↑Death-T occurred sometime between April and summer 1997. Gozaburo died six months earlier, meaning he died in 1996 or 1997.
↑Yugi is his first year of high school and is still in first year next summer, so this event takes place between the start of the Japanese school year, April, and summer.
↑Two months before Egypt Unearthed, a newspaper gave 1996 as the year. If this event takes place between April and summer, it would have been the same year as it was two months previously.
↑The Domino High school festival is mentioned as being bunkasai, the Japanese cultural festival. This event usually takes place in autumn. However individual schools may host it at any time. If the Domino High festival had taken place in autumn, it would result in contradictory information about the characters' school grades
↑ 30.030.1Yugi's class is mention as being 1-B, implying he is in first year of high school.
↑In a flashback from two months earlier, the Japan Daily News mentions 1996 as the year.
↑Pegasus and Keith's Duel took place after Dark Yugi and Kaiba's Duel, but before Death-T, evidenced by Kaiba beginning to develop Solid Vision. When it occurred in relation to other events between those two dates is uncertain.
↑Starting this chapter, characters wear the summer variation of their school uniforms.