Not registered to vote yet in the US? There’s a good chance you can still cast a ballot | Laura W Brill

With election day just a week away, candidates are ignoring millions of young Americans who could still cast a decisive ballot but have not yet registered to vote.

By contrast, my mailbox has been full of political flyers: the various campaigns gleaned my name from the voter file, recognized that I am a regular voter who hadn’t cast a ballot yet, and assessed through their targeted analysis that it’s worth spending on printing and postage to get their message to me.

Honestly, they are wasting their money on me – I have voted now and would have done so anyway, with or without their glossy mailers. What they should be doing is targeting people who are probably way more persuadable than I am, yet are routinely ignored: the millions of Americans who will be old enough to vote for the first time this November.

In California alone, for example, there are nearly 300,000 eligible 18-year-olds who can legally show up through election day and cast a provisional ballot. Their votes would count the same as mine. So why are their mailboxes empty?

It’s not just the 18-year-olds. We estimate that more than 1 million young Californians ages 18-24 who have not yet registered and are therefore not in the voter file still have a right to vote on election day or during early voting. And it’s not just California. More than half of US states allow eligible voters to cast provisional ballots either on election day, during some part or all of their early voting period, or both.

We estimate that 1.7 million 18-year-olds live in the 22 states (plus Washington DC) that allow voters to register on election day. Voter files show that almost half of them have not yet registered, so are probably not receiving mail from campaigns.

Across the country, only 45% of 18-year-old Americans are registered to vote, compared with 82% of the over-45s. It’s not apathy or laziness that stops them – it’s more often that no one bothered to ask them or explained how to do it and why it matters – including the candidates.

That’s despite the more than $10bn already spent in this campaign. Imagine if just 0.01% of that were spent building the on-ramp to democracy instead of on throw-away mailers and tune-out ads.

Four other states allow provisional voting during all or part of their early voting period for those who aren’t yet registered, but don’t allow it on election day itself: Massachusetts, Nebraska, New York, North Carolina.

You might wonder: does election day registration really matter for first timers? The answer is – absolutely. We looked at the voter files for a sample of four states with same-day registration on election day and they all see far more 18-year-olds making it into the voter file on that final day versus any other day of the year.

And this really should not be a surprise, but turnout correlates positively with allowing voting for eligible voters who haven’t signed up in advance.

Young people – because they are registered at such low rates and therefore aren’t targeted by candidates – often become aware of elections in the final weeks of campaigns, as more and more money is spent on advertising. In many states though, that is well after early registration deadlines. Plus they are highly mobile compared with other age groups, making early registration more challenging for them. The result is millions of voices left unheard, cycle after cycle.

We need to rebuild the systems that bring young voters in and that will take time, money and vision. But in the next few days leading to 3 November, we can all reach out to the people we know in the same-day states and encourage them to register and vote. It’s not too late for them to have their say and it’s never too early to start the habit of voting.

• Laura W Brill is the founder and CEO of the Civics Center, a non-partisan non-profit with a mission to make voter registration a core part of high school