Come July 2017, the same polling company put her on -7, while in June she had almost completely reversed her rating with a different company, polling -34 per cent approval from YouGov.
A similar dip happens with most leaders, particularly because once they're in power they have to start making decisions and that means somebody, somewhere, is going to be disappointed.
All prime ministers lose something once the honeymoon period wears off, but according to this comparison, May has had one of the biggest drops.
Comparing the Ipsos MORI net satisfaction score during the first 12 months of British prime ministers, the Daily Telegraph found Theresa May's popularity went south by the largest amount.
As each poll was conducted one month into their premierships, there are 11 results for each prime ministers' first 12 months in the above chart.
Of the last four leaders of the country, May has had the worst fall.
While Gordon Brown was the only Prime Minister of the four to increase his net satisfaction after 12 months in office, he was working from a low baseline of -16 when he took power in June 2007, raising it to -9 a year later.
By contrast his successor David Cameron, despite losing 34 points, was still more popular than Brown one year in, with -3.
It's worth nothing that Tony Blair finished a year into the job just one point below where Theresa May began.
Further to fall
By looking at how each of their ratings changed month to month, you can see that Gordon Brown almost had a simple bell curve. His popularity declined and then improved almost at the same rate it had been declining.
Theresa May by contrast had a much more erratic net satisfaction rating.
Significant political events could be one explanation for May's ups and downs.
In September 2016 her push for Grammar Schools coincided with a big drop down (16), then her visit to meet Donald Trump in January (6), and then an up tick when the Supreme Court caused a stir when they ruled on Brexit (17).
Similarly triggering Article 50 gave May another boost (up to 19), which was more or less sustained until the Tory manifesto and the 'dementia tax' debacle during the general election.
Now 12 months in, May has only just dipped into negative figures. Her immediate predecessor Cameron did this during his seventh month.
So at least that's something for the Prime Minister to be pleased about.