But the country's national statistics bureau has predicted the actual date with pinpoint detail: The world's most populous nation would officially hit 1.3 billion on 6 January.
And so it did, when a baby boy was proclaimed China's 1.3 billionth citizen at two minutes after midnight today.
For the average person, it's a figure that's difficult to comprehend. But population watchers look at it differently. For them, the number illustrates China's success in controlling its birthrate.
"In 1950, [China] had six children per woman," said Carl Haub, a demographer with the Washington-based Population Reference Bureau. "In 1970, it was just under five. So it was quite a high-fertility country. And by 1980, that figure was cut in half, to about 2.5 children. And then today, of course, it's 1.8. So that's quite a reduction."
China's so-called one-child policy was instituted in 1979 in response to the Communist government's fears that a population explosion would eventually lead to widespread famine.
The plan imposed strict limitations on the number of children each family could have. It did not literally limit all couples to just one child. Families in rural areas, for example, were sometimes allowed to have two, particularly if the first was a girl. No limitations were officially imposed on national minorities living in the country's west, though limits were often instituted on minorities by local and regional officials.
Throughout most of China, the policy was rigorously enforced. The government officially was to provide free birth control and abortions, and offered added incentives to couples who pledged to have just one child.
It also was strict in punishing those who failed to comply. Chinese women were often forced to abort pregnancies, or even to be sterilized. Men faced beatings or demotions if their wives bore too many children. Some Chinese were even sentenced to jail terms for violating the policy.
But if government leaders were merciless in imposing the one-child rule, in the end, the results were what they wanted.
In just 25 years, China's birthrate has dropped sharply. The threat of a population explosion has vanished. China's Xinhua news agency reports the policy even succeeded in postponing the 1.3 billion milestone by four years.
Moreover, many Chinese appear to have embraced the change. The one-child era has coincided with a period of strong economic growth in China.
More and more women are entering the workforce and marrying later. For many young couples -- particularly in urban areas -- the goal is no longer a large family but a large bank account.
"As people -- especially young people -- are becoming a little more well off, some of the same things that have happened in Western countries are happening here in terms of a desire for smaller family size," said David Osterhout, a journalist who for the past five years has lived in Shanghai. "That's driven by the fact that a lot of young people are in two-career households and it just works better with their lifestyle, the fact that they need to save money for an apartment and all the elements of an increasingly middle-class society. You know, frankly, I don't hear a lot of Chinese people saying that they're really against the one-child policy. For many, one is enough."
The one-child policy has proved an economic asset in other ways as well. China's slow population growth means government spending on schools and other social infrastructure has remained steady for nearly two decades. Instead, the state has been able to focus much of its spending on building up the country's industrial sector.
Athar Hussain, deputy director of the Asia Research Center at the London School of Economics, said this has allowed the country to prosper economically with no sacrifice in educational standards.
"One great positive effect [of the one-child policy] is that the number of school-age children is about the same as it was in 1982," Hussain said. "And in a developing economy, that is very important because educating the population is by far the most important issue. And we know from South Asia or other countries where the population growth rate has been higher, the government has to spend more and more money just in order to keep [education] at the same place. So as a result, the Chinese -- both parents and the government -- are able to invest in the education of children. They are investing in quality -- they don't substitute quality of education for quantity."
China's one-child policy has its negative side as well. It has imposed the distinctly unromantic hand of the government onto what was once a personal family matter.
It has also spawned the widespread practice of selective abortion using sonograms and amniocentesis to determine a fetus's gender. The desire for a son is so strong in China that many women limited to one child will have repeated abortions until they can be certain of having a boy.
Some observers also say the one-child policy has contributed to a rise in female infanticide and abandonment. The World Health Organization said in a report in 1997 that "more than 50 million female infants were estimated to be 'missing' in China because of the institutionalized killing and neglect of girls due to Beijing's population control program that limits parents to one child."
Other organizations say selective abortion and underreporting of girl babies have been the predominant response to the government's population-control program. A ban on selective abortion exists, but is rarely enforced. Chinese media, however, report the government is taking steps to make such abortions a crime.
The 1.3 billion mark might be one of China's last population milestones. At the current average of 1.8 children per household, the Chinese population is due to peak at 1.45 billion within the next three decades.
By 2050, it will have even begun to shrink in size. By then, the world's most populous nation is expected to be India, with a projected 1.6 billion people.
See Part 2 of this series: A Future With A Shortage Of Brides, An Abundance Of Elderly