The dodo probably died out in 1690, nearly 30 years later than the last confirmed sighting of the bird.
One of the few dodo heads left in the world
Some of the flightless birds survived unseen for decades, according to a statistical analysis by scientists reported in the journal Nature.
The last confirmed sighting of the dodo was in 1662 on Mauritius.
By then the species had long been in decline, driven to extinction by humans and the predators they took to the Indian Ocean island.
All that remains of the dodo now are the odd skeleton and other body parts, such as head and feet, scattered around the world in museums.
Fragments of DNA have been extracted from the bones, shedding light on its evolution.
The dodo (Raphus cucullatus), which was bigger than a turkey, weighing in at about 23 kilograms, was uniquely adapted to its island habitat.
The dodo was first seen by Portuguese sailors about 1507 but numbers were falling sharply by the beginning of the 17th Century.
Forest-dwelling and flightless
Waded in ponds to catch fish
Killed by sailors for extra food
Ship animals stole its eggs
A pair of researchers, from the UK and the US, used the 10 most recent sightings of the bird, from 1662 to 1598, to calculate when it might have died out.
It was a statistical analysis and it suggested the last dodo died not in 1662 but 28 years later, in 1690.
It has always been assumed the bird was long gone by 1681.
The mathematical method the team used could shed light on when other extinct animals, like the dinosaurs, met their demise, using dates from the fossil record rather than sightings.
It might even be possible to predict how long existing threatened species, which have been seen only sporadically in recent years, might survive.
"In most cases, the extinction of a species can be inferred from the record of sightings or from collections of individual organisms," co-authors David Roberts of the Royal Botanic Gardens in south east England and Andrew Solow of the Woods Hole Oceanographic Institution, Massachusetts, write in the journal Nature.
"But when a species becomes increasingly rare before its final extinction, it may continue to exist unseen for many years - so the time of its last sighting may be a poor estimate of the time of extinction."