Parents have been oblivious to a size rule that could have stopped their babies' nappies leaking, according to one mum.
Like most parents, Manchester mum Nicci Pearce thought the plus symbol on packs of nappies meant that it was a half size - with 4+ for example being a step up between four and five.
But it turns out that she, along with thousands of other experienced parents, have been getting it wrong all this time.
The + sign is actually an indicator of added absorbency .
The mum-of-two shared a post about the meaning of the symbol on Facebook saying: "Who knew this? I always thought the plus ones went up higher on the back."
And she got a huge reaction from mums who'd always thought the same thing.
Nicci, mum to Ava, two, and nine-month-old Calel told the Chronicle's sister paper Manchester Evening News: "Ava is toilet training now, but all the time she's been in nappies I've always gone up 3, then 3+, then 4, then 4+ then 5 and so on."
Another mum who replied to Nicci's post said: "I thought the plus sign was that the nappy was just that bit slightly bigger."
The information about the sizes is actually available on the manufacturers' websites, but understandably has passed most busy parents by.
In a response to a customer's complaint on its website about their child's nappy leaking, Pampers reiterates the size guidance.
It states: "I know leaks can be a nightmare, but usually by either changing to a different style, or to a nappy which offers a little added absorbency this can be prevented.
"We have learnt over the years that all little ones, just like us adults, have their own unique shapes, so you may find one style of nappy to be better suited to your little one, compared to another.
"They can also outgrow the absorbency before the size, so we do offer plus sizes too, which will offer a little added absorbency."
So now you know. More absorbent nappies could save you plenty of time and money - so you'd best tell all your parent friends too.