Why is it often changed later?
The UK produces one of the quickest estimates of GDP of the major economies, about 40 days after the quarter in question.
At that stage, only about 60% of the data is available, so the figure is revised as more information comes in.
The ONS publishes more information on how this is done on its website.
What are its limitations? pg
GDP growth doesn't tell the whole story.
There are lots of things the statistics might not take into account:
Hidden economy: Unpaid work isn't captured in official figures, such as caring for an elderly relative
Inequality: GDP growth doesn't tell us how income is split across a population - rising GDP could result from the richest getting richer, rather than everyone becoming better off
Just because GDP is increasing, it doesn't mean that a citizen's standard of living is improving.
If a country's population increases, that will push GDP up, because with more people, money will be spent.
However, the individuals within that country might not be getting richer. They may be getting poorer on average, even while GDP goes up.
So the ONS publishes a figure for GDP per head (of population), which can often tell a different story to the main GDP number.
Critics have argued that GDP doesn't take into account whether the economic growth it measures is sustainable, or the damage it might do to the natural world.