The Human Genome Project was completed two years ahead of schedule. It was originally expected to take 15 years, beginning in 1990 and finishing around 2005, but the essentially complete sequence was announced on April 14, 2003.
The early completion reflected rapid improvements in DNA sequencing, automation, computing power, and international coordination. Competition from Celera Genomics also pressured the publicly funded consortium to accelerate its work. A rough draft had already been announced in June 2000, and draft genome papers appeared in 2001.
The 2003 milestone covered about 92% of the human genome, chiefly the euchromatic regions targeted by the original project. Highly repetitive heterochromatic regions, including difficult centromeric and telomeric DNA, remained unfinished. Later research eventually closed many of those gaps, with a truly gapless human genome sequence arriving decades after the project began.
The phrase “completed” therefore refers to the project's planned reference sequence, not to every base of DNA in the human genome. That distinction explains why later genome-finishing efforts were still necessary.