At least £2.1bn worth of old £10 notes need to be spent or exchanged before they cease to be legal tender, the Bank of England says.
The deadline to spend or exchange old £10 notes – featuring naturalist Charles Darwin – is 1 March.
Plastic polymer tenners depicting author Jane Austen entered circulation in September.
Currently, weekly returns of paper £10s are averaging at a value of £85m or 8.5 million notes, according to the Bank.
To exchange an old tenner, people can either post the notes to the Bank of England, or visit the Bank in person in the City of London.
The Bank will exchange all old £10 notes indefinitely.
The Bank says people can also try to exchange paper tenners at their local bank or post office.
However they are not legally required to accept old notes after the deadline.
The Bank does not expect all old £10 notes to be returned, because some will have been destroyed, gone overseas or kept as memorabilia.
Counterfeiters do not seem keen on targeting old paper £5s and £10s, according to the Bank.
In 2017, just 0.0054% of all ten pound notes were found to be counterfeit, and much less for the fiver at 0.0002%.