Want a big family? Then you need to start aged 23: Scientists develop fertility predictor which warns against leaving motherhood too late .

Women who want to have a big family should start trying for a baby by 23, experts have warned.

Even those who only want one child shouldn’t wait past the age of 32, if they really want to become a mother.

The advice comes from scientists who crunched together fertility data on more than 58,000 women to create an at-a-glance calculator.

It tells a woman the best age to start a family – and makes it clear that IVF is not a guarantee for those who wait.

British experts said that the table is so useful that it should be shown to sixth formers and university students to underline the risks of delaying motherhood.

Professor Allan Pacey, a Sheffield University fertility expert, said: ‘We haven’ t got a time machine we can put people in….that’s just a blunt reality.

‘Everyone thinks you can wait – this shows you can’t.’

The advice comes as growing numbers of British women delay motherhood until they establish their career, become financially stable or find ‘Mr Right’.

Around half of all babies are now born to women aged 30 and older, and the number of children born to women aged 40-plus has trebled in the last 20 years

To use the fertility calculator, a woman decides how many children she wants and whether she is going to try to conceive naturally or with IVF.