"Forty, Counting Down"  
Asimovs Dec1999.jpg
Author Harry Turtledove
First Appearance Asimov's
Collected Counting Up, Counting Down
Series Justin Kloster Stories
Genre(s) Science fiction
Publication date December 1999
Followed by Twenty-One, Counting Up

"Forty, Counting Down" is a science fiction short story involving time travel, written by Harry Turtledove. It first appeared in the December 1999 issue of Asimov's. This same story is also told in the story "Twenty-One, Counting Up" but from the protagonist's younger perspective. It is available in the collection Counting Up, Counting Down. In 2000, "Forty, Counting Down" was nominated for the Hugo Award for Best Novella.

Turtledove insists in the Counting book that the Justin Kloster Stories can be read in any order, and refuses to say which was written first.

In this story set in the near future, 40 year old computer genius Justin Kloster invents a time-machine based on string theory and virtual reality. Using this device, he travels back in time to visit himself when he was 21. It was at this age that he began dating his future wife who later divorced him. As Justin never recuperated from this loss, he decides that this time-machine is his chance to redo his relationship with her with more success. As such, he convinces his younger self to lay low while his older self (who happens to have aged very well) courts his girlfriend. Unfortunately for Justin's plan, he finds that his older self is even less successful than his younger one, and his girlfriend leaves him, much sooner than she did in the original timeline. The older Justin decides to return to his own time in the future, leaving behind a large sum of money. When he awakes in his original time, he discovers that he has successfully founded his own string-theory company, and is happily married to a rediscovered sweetheart from his distant past and has two sons. He attributes this to his original relationship not becoming as serious, as well as inspiring his younger self and providing him with seed-money to start his own business.