There are a "missing eight million" women who won't vote in the general election on June 8.
Shocking figures compiled by the Fawcett Society, the UK's leading charity for gender equality, also reveal that fewer women than men are registered to vote.
An average of recent polling shows that 2.5% points fewer women than men say they are certain to vote.
When applied to turnout at the 2015 general election this could see eight million women not exercising their rights, half a million more than the 7.5 million men who are not certain they’ll vote.
There is also a gap in voter registration with 2.5% points fewer women than men saying that they are currently on the register.
With the deadline to register to vote just two weeks away, the charity is warning that millions of women won't be able to have their say almost a hundred years after women won the right.
The charity is also urging candidates to take on board their women's manifesto.
Fawcett Chief Executive Sam Smethers said: “Almost 100 years on from the first women getting the right to vote, we still see what is likely to be a significant gap in turnout by gender.
"We are calling on all women to make sure they register to vote before the deadline.”
“With the overall gender pay gap still at 18%, violence against women and girls still rife in our society, and Brexit posing a risk to hard-fought protections, it is as important as ever that women have a say.
"We urge women across the country to take these demands to their candidates.”
Fawcett analysis also shows that, across different polls, women have different priorities to men in the general election.
Women consistently view the NHS as a more prominent issue, with 63% in an average of polls saying it is key compared with 50% of men.
Men are slightly more concerned with Brexit , with 50% rating it as an important issue versus 45% for women.
The charity’s manifesto calls for measures to get more women into power, including for at least 45% of parties' parliamentary candidates to be women.
Other key recommendations include:
· Women to be represented at every level and stage of Brexit negotiations.
· An increase in the national living wage to bring it up to the level of the real living wage.
· An extended, dedicated, well paid period of leave for fathers
· A requirement for large companies who have to report their gender pay gaps to have an action plan in place, and penalties for those who do not comply.
· A long-term, national, and sustainable funding strategy for specialist women-only services including domestic violence refuges, in order to meet our Istanbul Convention obligations.
· A National Care Service, giving social care parity with the NHS, and investing in social care infrastructure with a professionalised care workforce.
The Manifesto also addresses equal representation, defending women's rights post- Brexit , ending violence against women and girls, and ensuring women are not hardest hit by any economic downturn or spending cuts.
How do I register to vote?
Visit gov.uk/register-to-vote and fill in 11 questions.
They include your name, address, National Insurance number and whether you want a postal vote.
There's not much else you need to fill in.