Estimated reading time: 7 minute(s)

I recently read an interesting fact that surprised me on the first instance: The incumbent President, Joe Biden, was born closer to the assassination of Abraham Lincoln than to his own inauguration. (Sadly – I forget the source for the fact.) I checked the relevant dates after reading the fact and confirmed that it was indeed true. That discovery, combined with our own website’s recent birthday, inspired me to undertake a study. If we take the amount of time between Mr. Biden’s birth and his inauguration and count backward from his birth using that same amount of time, the resulting date falls on September 20, 1864, during the presidency of Abraham Lincoln. What if we repeated this process for every U.S. president for whom the relevant “count-back” date is April 30, 1789 (the inauguration of George Washington), or later? This survey answers the following question: If we take the time that elapsed between a president’s birth and his first taking office and count backward from his date of birth using that time, who was president at the resulting date?

Photograph of Ulysses S. Grant from 1869.
Photograph of soon-to-be-President Ulysses S. Grant taken in 1869, the year that he assumed the presidency. Grant will feature somewhat prominently in our survey. Source.

Let us find out. Before continuing, I stop to note that you may also be interested in my 2020 article on presidential birthday facts.

May 7, 2022 Update: I calculated the earliest presidential count-back date without the limitation of only considering presidents whose count-back dates are later than George Washington’s April 30, 1789 inauguration. I published the result in a leaflet which summarized my full-length post at NAF Musings.

Survey Rules

In this survey, I will undertake the following calculations:

  • Take the date of birth of the U.S. president
  • Determine how much time elapsed between the president’s date of birth and his first taking the oath of office
  • Take the time that elapsed from the president’s date of birth to his inauguration, and count backwards starting from his date of birth (“count-back date”)
  • Determine who the president was on the applicable count-back date

Let us apply the above to the case of Mr. Biden.

  1. Mr. Biden was born on November 20, 1942
  2. Mr. Biden was inaugurated as president on January 20, 2021
  3. 78 years and 61 days elapsed between Mr. Biden’s birth and his inauguration
  4. The date 78 years and 61 days before Mr. Biden was born was September 20, 1864
  5. Abraham Lincoln was the President of the United States on September 20, 1864

The results for each president will be determined by (A) when the president was born and (B) how old the president was when he took office.

Two notes before we get to the list:

  1. I will list when each president first took the oath of office. This allows us to better account for presidents who ascended to the office from the vice presidency than using inauguration as the pertinent date. Moreover, we do not want to exclude Gerald Ford, who did not win a term in his own right.
  2. In the case of two-term presidents, I will only use the date on which they were first sworn in. For example, while Barack Obama and Ronald Reagan both won two terms, I will use the date on which they were first sworn in as the pertinent date for the survey.
  3. I will not perform the calculations for presidents where the result would be a date prior to the inauguration of George Washington. Only Presidents 26-46 (beginning with Theodore Roosevelt), produce a qualifying result for the survey. The first 25 presidents do not produce qualifying results (the 25th president, William McKinley, barely missed the cutoff with a count-back date in December 1788).


No.PresidentDOBSworn InTime ElapsedCount-Back DateCount-Back President
46Joe Biden11.20.19421.20.2178 y, 61 d9.20.1864(16) Lincoln
45Donald Trump6.14.19461.20.1770 y, 220 d11.7.1875(18) Grant
44Barack Obama8.4.19611.20.0947 y, 169 d2.16.1914(30) Wilson
43George W. Bush7.6.19461.20.0154 y, 198 d12.21.1891(23) B. Harrison
42Bill Clinton8.19.19461.20.9346 y, 154 d3.18.1900(25) McKinley
41George H.W. Bush6.12.19241.20.8964 y, 222 d11.3.1859(15) Buchanan
40Ronald Reagan2.6.19111.20.8169 y, 349 d2.22.1841(8) Van Buren
39Jimmy Carter10.1.19241.20.7752 y, 111 d6.12.1872(18) Grant
38Gerald Ford7.14.19138.9.197461 y, 26 d6.18.1852(13) Fillmore
37Richard Nixon1.9.19131.20.196956 y, 11 d12.29.1856(14) Pierce
36Lyndon Johnson8.27.190811.22.196355 y, 87 d6.1.1853(14) Pierce
35John Kennedy5.29.19171.20.196143 y, 236 d10.5.1873(18) Grant
34Dwight Eisenhower10.14.18901.20.195362 y, 98 d7.8.1828(6) J.Q. Adams
33Harry Truman5.8.18844.12.194560 y, 339 d6.4.1823(5) Monroe
32Franklin Roosevelt1.30.18823.4.193351 y, 33 d12.28.1830(7) Jackson
31Herbert Hoover8.10.18743.4.192954 y, 206 d1.17.1820(5) Monroe
30Calvin Coolidge7.4.18728.2.192351 y, 29 d6.5.1821(5) Monroe
29Warren Harding11.2.18653.4.192155 y, 122 d7.3.1810(4) Madison
28Woodrow Wilson12.28.18563.4.191356 y, 66 d12.28.1799(2) Adams
27William Howard Taft9.15.18573.4.190951 y, 170 d3.29.1806(3) Jefferson
26Theodore Roosevelt10.27.18589.14.190142 y, 322 d12.10.1815(4) Madison
Wikipedia has a useful resource listing the pertinent ages of each president.


I did not know what to expect when I began my survey. The biggest shifts in the survey occurred when a president who was unusually young or unusually old took office. For example, our list begins with Theodore Roosevelt, who was the youngest president to ever take office when he ascended from the vice presidency upon the death of William McKinley. Prior to Roosevelt, no president had a qualifying count-back date (although I noted that McKinley was close). Theodore Roosevelt was so young that the first count-back date fell within the 8-year presidency of the fourth president, James Madison. We would not have a count-back date that landed later than Madison until Calvin Coolidge took office 22 years later.

John Kennedy, the youngest president to win a term in his own right, marked a paradigm shift. He moved the count-back date forward 43 years from the previous latest (Franklin Roosevelt’s 28 years earlier). Kennedy became the first of three presidents (Carter 1979 and Trump 2017) to record a count-back date falling in the 8-year presidency of Ulysses S. Grant. That Kennedy’s count-back was within two years of Mr. Trump’s and later than Mr. Biden’s, who took office 56 and 60 years, respectively, after Kennedy is certainly striking.

The last two shifts are young and old. Prior to Mr. Trump in 2017 (and subsequently Mr. Biden in 2021), Ronald Reagan was the oldest president to take office. He was the last president to have a count-back date falling within the term of one of the first ten presidents (Martin Van Buren). While I will demonstrate at the end of this article that it is not impossible for another president to have an earlier count-back date than Reagan, it is certainly unlikely.

The two most recent count-back dates are owned by Bill Clinton and Barack Obama. Mr. Clinton was the second-youngest president to win his own term in office behind Kennedy, so there is little surprise there. Mr. Obama was a few years older than Mr. Clinton when he took office, but currently owns the most recent count-back date due to the fact that he took office 16 years after Mr. Clinton.

My final notable point. A good way to study the effects of the count-back date math is to look at Mr. Clinton, Mr. George W. Bush, and Mr. Trump. These three presidents took office in 1993, 2001, and 2017, respectively. What is notable about them is that they were born within a few months of each other in 1946 (Mr. Trump is the oldest followed by Mr. Bush and Mr. Clinton, respectively). Mr. Trump and Mr. Clinton took office 24 years apart – and the chart demonstrates the effect that this difference had on their count-back dates after starting from almost the same birthday.

Note: I looked at two interesting near-misses involving losing general election candidates who were in their 70s. Had Bob Dole won the 1996 election, he would have posted a count-back date of January 19, 1850, landing during the truncated term of the 12th president, Zachary Taylor. Had John McCain won in 2008, his count-back date would have been April 6, 1864, falling during the presidency of Abraham Lincoln.

The Jimmy Carter Hypothetical

The 39th president, Jimmy Carter, is currently the oldest-living ex-president in history. Mr. Carter only served one term, meaning that he is eligible under the Constitution to serve another. Now Mr. Carter is obviously not running for president in 2024, but let us pretend that he decided that the time was right to try to win the second term that he failed to secure in the election of 1980. Let us take another step and imagine that Mr. Carter actually won his second non-consecutive term in 2024. Because Mr. Carter would not be serving a consecutive term, he would be entitled to a new count-back date. Given his age, this hypothetical provides a reasonable idea of how far we could push the count-back date in the next election. Let us see what the result would be:

  • Mr. Carter was born on October 1, 1924
  • In this hypothetical, Mr. Carter is taking office (again) on January 20, 2025
  • 100 years and 111 days elapsed between Mr. Carter’s birth and (second) inauguration
  • Mr. Carter’s count-back date would be June 30, 1824
  • The president on June 30, 1824, was James Monroe

Thus, Mr. Carter (or a similarly-situated 100-year old president-elect) would produce the earliest count-back date since Harry Truman assumed the presidency in 1945. Mr. Carter’s count-back date would also be almost identical to Calvin Coolidge’s, who took office in 1923 – and earlier than Franklin Roosevelt’s, who took office in 1933. While I can confidently say that our next president will not be 100 (although we might not be too far off at the current rate), this thought-experiment provides an example of how far the count-back date could theoretically be pushed in the 2024 election.