https://pmc.ncbi.nlm.nih.gov/articles/PMC8294566/
Surveys conducted over the last few years on representative samples in the US and Germany suggest that the percentage of parents who regret having children is approximately 17–8%.
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The results obtained show that the percentage of parents who regret parenthood is higher in Poland than in the US or Germany, and that parents who regret having children are characterized by a higher level of adverse childhood experiences, have poorer psychological and somatic health, are more vulnerable to social evaluation, and experience strong parental identity crisis and parental burnout. Regretting parenthood also turns out to be associated with the parent’s financial situation and marital status, and with having children with special needs.
https://www.psychologytoday.com/gb/blog/your-future-self/202310/if-you-regret-parenthood-researchers-say-youre-not-alone
The team of researchers who conducted the study highlighted past research showing that regret over having children isn’t rare or unheard of, as 5-14% of parents have this feeling. They also noted that social disapproval around this topic, alongside the absence of ways to assess regret over parenthood, are both factors behind the relative scarcity of research in this valuable area. To address this issue, they created and tested an assessment known as the Parenthood Regret Scale. They translated it across three languages (i.e., Polish, French, and English) and found that it’s a reliable and valid measure.
In their research with this scale, they found a link between regret over parenthood and parenting burnout, depression, and contentment with one’s life. Specifically, more parental regret was connected to less happiness with life and more parenting burnout and depression
https://www.independent.co.uk/life-style/love-sex/parents-children-regret-yougov-survey-b1871964.html
Data from YouGov shows that although the vast majority of parents (83 per cent) say they have never felt regret about starting a family, eight per cent say they regret it, while another six per cent previously had regrets but don’t now.
YouGov surveyed 1,249 parents and found that not all who regret the decision to become a parent feel the same way forever. One in seven regretted having children at some point in their lives, compared to one in 12 who said they still regret it.
The figures are higher than I thought they'd be - and I wonder as financially it's got harder in many countries and socially less support from families and as work hours and commutes have got longer the number have it's increased.