Baby names starting with O: girls and boys

The most used girls' names beginning with O in 2025

O is the letter that reaches highest and runs out fastest. Olivia is the most popular girls' name in England and Wales, given to 2,386 babies, and it accounts for 35 per cent of every girl given an O name. Behind it the letter has only 151 distinct spellings in total, the ninth-smallest set in the alphabet, covering 6,873 babies.

The most used boys' names beginning with O in 2025

For boys the letter is larger and slightly better spread: 12,486 babies across 198 names. Oliver at 3,154 and Oscar at 2,798 are sixth and eighth in the country, and Oakley at 1,377 is a recent arrival at 33rd. Four O names sit inside the boys' top 100, and after Otis at 726 the letter drops away sharply.

Which O names are rising and which are falling

Climbing

Ottilie gained 16 places to 55th, the letter's biggest single-year climb, and Olive gained 6. Both have moved enormously over ten years: Ottilie is up 357 places since 2015, the fourth-largest rise in the girls' top 100, and Olive 128. Among boys Oscar gained a place and Oakley a place, and Oakley is up 133 places since 2015 and Otis 188.

Slipping

Ophelia fell 8 places, Orla 6 and Oliver 3. Otis lost 4 places despite its very large ten-year gain. Olivia itself did not move: it held first place in 2025 and is one place higher than it was in 2015, which after a decade at or near the top is the flattest line in the entire girls' dataset.

What the published change columns cannot tell you

Ocean, Octavia, Orlaith, Opal, Oliwia, Ollie, Omar, Owen, Ozzy and Osian are all outside the top 100 and have counts but no published change. Osian at 165 is the clearest case of a name that would look very different in a Wales-only table, since it is a Welsh name and the ONS publishes separate Wales figures within the same release.

How big a letter O really is

O is fourteenth for girls and ninth for boys by babies, but eighteenth and fifteenth by number of distinct names. That combination, high volume and few names, makes it one of the most concentrated letters in the alphabet: three names, Olivia, Oliver and Oscar, account for 8,338 babies between them, more than every girl in England and Wales given a name beginning with P.

There is almost no middle to the letter. On the girls' side, below Ophelia at 578 the next name is Ocean at 143, a drop of more than four hundred babies in a single step, and the rest of the list is in double figures. Very few letters fall away that steeply, and it means an O name is either extremely common or genuinely rare with little in between.

Further O names in the published 2025 list

The ONS full list does not stop at the tables above, and the counts stay exact all the way down. For girls the next names in order of use are Olympia at 38, Oakley at 29, Oriana at 28, Orlagh at 28, Ottillie at 27, Oluwadarasimi at 26, Oluwatamilore at 25, Ottie at 21, Oona at 20, Olivia-Grace at 19, Olivia-Mae at 19, Olaedo at 18. For boys they are Orion at 113, Orson at 109, Orlando at 85, Odin at 84, Osman at 82, Oisin at 75, Olly at 54, Omari at 54, Ovie at 50, Omer at 48, Ozzie at 40, Ocean at 36. Each figure is the exact number of babies registered with that exact spelling during 2025, taken from the ONS full-list table rather than from the top 100. The letter carries 151 different girls' names and 198 different boys' names in the published data altogether, and any name given to two or fewer babies has been removed from it.

Choosing a O name: what the data changes

If you want the sound of Olivia without the frequency, the ONS list gives you Olive at 892, Ottilie at 782 and Oliwia at 46, and all three are counted separately from Olivia itself. For boys, Oliver and Oscar together were given to 5,952 babies in one year, so both should be treated as top-ten choices rather than as distinctive ones.