At least some content in this article is derived from information featured in Harry Potter: Hogwarts Mystery. Spoilers will be present within the article.
Underage magic was any magic used by a wizard or witch who was under seventeen years of age outside of school. While children were permitted to use magic as part of their education, it had been banned from use outside of such under the Decree for the Reasonable Restriction of Underage Sorcery since 1875. Compliance with the Decree was monitored and enforced by the Improper Use of Magic Office at the British Ministry of Magic using the Trace Charm. Children under the age of eleven, who had little control over their abilities and no wands, were exempt from the law. Though in wizarding families their parents were expected to keep them under control. The British Ministry of Magic could only detect where magic was used, but not who used it. Most experts believed that if a child had magical ability, they would exhibit it by the age of seven.
Accidental wandless magic
Magical children were prone to using magic accidentally when feeling angry, scared, or confused, as a form of self-defence. They typically had no control over this magic.
- Ariana Dumbledore was attacked by Muggle boys after they saw her performing magic, and the trauma affected her to the point of preventing her from ever learning to control her magic. In one of her fits, she accidentally killed her mother in a magical explosion.
- As a boy, Severus Snape made a branch of a tree snap and strike Petunia Evans in the shoulder when she made fun of him.
- Before Harry Potter went to Hogwarts, he did several things accidentally using his magical powers. He turned his teacher's wig blue, shrunk one of Dudley Dursley's old sweaters that Aunt Petunia was trying to force him to wear, and found himself on the roof once when his cousin Dudley and his gang were chasing him; possibly through a form of Apparition. He managed to grow all his hair back when his Aunt Petunia gave him a dreadful haircut using a pair of kitchen scissors. He also magically spoke with a Boa constrictor at the Zoo in Parseltongue and unintentionally set it free by making the glass vanish. In 1993, he lost control of his magic when Marge Dursley insulted his late parents; his anger caused her to magically inflate.
- As a newborn, Neville Longbottom magically adjusted his blankets so that he was swaddled more snugly, but nobody noticed. Later, his uncle, Algie Longbottom accidentally pushed him out of a second story window in one of his many attempts to get Neville to perform magic. Luckily, on this occasion, he did and bounced away instead of hitting the ground in what would have been a terrible fall otherwise. 
- During their childhood, Jacob's sibling shattered a tea set and vase when they sneezed, and brought a flower to life with their laughter.
Intentional wandless magic
- Tom Riddle: "It's... it's magic, what I can do?"
- Albus Dumbledore: "What is it that you can do?"
- Tom Riddle: "All sorts. I can make things move without touching them. I can make animals do what I want them to do, without training them. I can make bad things happen to people who annoy me. I can make them hurt if I want to... I knew I was different. I knew I was special. Always, I knew there was something."
- — Tom Riddle telling Albus Dumbledore of his magical abilities at eleven years of age[src]
Some magical children exhibited mild degrees of control over their magic and were able to use it with intent, but not to cast specific spells. The ability to perform specific spells without a wand was an advanced ability that even some adult wizards and witches found difficult. According to Albus Dumbledore, it was unusual and even somewhat worrisome for a child to be able to control their magic before the age of eleven. When discussing Tom Riddle's exceptional degree of control over his magic as a child, Dumbledore remarked that his powers were "surprisingly-well developed for such a young wizard and — most interestingly and ominously of all — he had already discovered that he had some measure of control over them, and begun to use them consciously".
- As a child growing up in an orphanage, Tom Marvolo Riddle developed remarkable control over his magic for his age, even before he consciously knew what the power was. He could manipulate the minds of animals and creatures (for the free will, thoughts, and minds of animals are quite weak), enchant objects to make them move or travel floating with his mind, inflict harm on those who annoyed him, and speak Parseltongue.
- As a baby, in the mid 1930s, Minerva McGonagall used to summon toys that had been left on upper shelves to her cot, made the family cat do her bidding, and made her father's bagpipes play themselves.
- Lily Evans displayed some control over her magical abilities as a girl. She floated off a swing set and manipulated the petals of a flower in front of her sister Petunia.
Underage magic with a wand
- "Dear Mr Potter, the Ministry has received intelligence that at six twenty-three, this evening, you performed the Patronus Charm in the presence of a Muggle. As a clear violation of the Decree for the Reasonable Restriction of Underage Sorcery, you are hereby expelled from Hogwarts School of Witchcraft and Wizardry. Hoping you are well, Mafalda Hopkirk."
- — Harry Potter's notice from the Improper Use of Magic Office in 1995[src]
British witches and wizards between the ages of eleven and seventeen were permitted to use magic within school, but not outside it, as legislated in the Decree for the Reasonable Restriction of Underage Sorcery. When any magical activity was performed in the vicinity of an underage individual, the Trace Charm notified the Improper Use of Magic Office as to the spell that had been used and its location. Small infractions of the law would be met with a warning, but knowingly performing magic in a Muggle-inhabited area or in front of a Muggle was considered a crime punishable by expulsion from Hogwarts School of Witchcraft and Wizardry, as it violated the Statute of Secrecy. Exceptions were permitted in exceptional circumstances, such as self-defence and other life-threatening situations.
According to Albus Dumbledore, although the Ministry could detect the use of magic near an underage witch or wizard, they couldn't determine who performed it. This was why Harry was blamed for the Hover Charm used by Dobby at his aunt and uncle's house; since Harry was the only wizard who lived there, the Ministry assumed he was the only one who could have cast the spell. In the home of a wizarding family, it was up to the adults to enforce the rules for underage members of the household (also according to Dumbledore). This was consistent with the relatively numerous incidences of underage magic mentioned as having been performed at home by Fred and George Weasley.
Also, an underage wizard or witch might perform magic outside of school if given permission by a recognised authority figure, as Dumbledore gave a sixteen-year-old Harry Potter permission to use any form of defensive magic during their journey to Budleigh Babberton in case of an attack.
Before 1965, in accordance with Rappaport's Law, magical children in America were forbidden to possess wands until age eleven, and could not use them outside of school before they reached the age of majority at seventeen. They were issued wands upon their arrival at Ilvermorny School of Witchcraft and Wizardry and had to leave them at school during vacations. It is unknown what the laws were after the law's repeal.
- Harry Potter received a warning after a Hover Charm was detected in his home in Little Whinging, though it was actually performed by Dobby the house-elf.
- In 1995, Harry used the Patronus Charm to ward off Dementors that attacked him and his cousin Dudley Dursley. He was expelled from Hogwarts for it, though this was rescinded in his Wizengamot hearing, as he was acquitted on the grounds of self-defence, and because the Ministry does not have the authority to expel Hogwarts students.
- Lily Evans occasionally used magic outside of school, despite living with her Muggle family, and received a few warning letters, but nothing “too serious”.
- Hermione Granger mentioned having successfully cast "a few simple spells" upon learning that she was a witch and before her first year at Hogwarts, but apparently she was not given a warning. This might have been because underage magic warnings only apply to Hogwarts students.
- In 1994, a boy named Kevin took his father's wand and enlarged a slug before his mum caught him.
- Sirius Black secured the decorations of his room with a Permanent Sticking Charm against alteration by his parents. As he left his parents' home at the age of sixteen, he must have performed underage magic.
- Hermione Granger used the Wand-Lighting Charm in the woods on the Quidditch World Cup grounds in 1994, though apparently due to the Death Eater activities, this seemed to have been counted as a measure of self defence and thus no warning was issued.
- On 27 June, 1997, Harry Potter used numerous spells during the Battle of the Seven Potters to defend against Death Eater attacks. No hearing was called as the Ministry apparently did not want to draw attention to Voldemort's current level of strength, nor that there had been a mass breakout from Azkaban. Even if this were not the case, it would certainly be counted as being in self defence.
Other underage magic
- At the age of five, Fred Weasley turned his younger brother Ron's teddy bear into a "great big filthy spider" after Ron broke his toy broomstick. This incident triggered Ron's lifelong fear of spiders. It is unclear if Fred did this without a wand and with some degree of control, or if he took the wand of one his parents or older brothers to perform the spell.
- In 1995, when gripped by his uncle, Vernon Dursley, Harry Potter emitted a defensive charge, apparently as an automatic defensive response.
- In 1995, at the age of fifteen, Harry Potter cast Lumos despite the fact that his cousin Dudley Dursley had punched him moments before and knocked his wand from his hand. The spell caused the wand's tip to light up. This was a specific spell, which differentiates it from the intentional wandless magic of children who have not yet learned spells, and it also involved a wand, though it was not in Harry's hand at the time.
- Nymphadora Tonks learned the Jelly-Legs Curse when she was little. It is unclear if she was able to perform controlled wandless magic, got her own wand at a younger age or used the wand of another person.
Behind the scenes
- Harry's early uses of underage magic, such as turning his teacher's wig blue, were cut from the film adaptation of Harry Potter and the Philosopher's Stone, presumably for time reasons. The only visible incidents are his speaking Parseltongue with the Boa constrictor at the Zoo (depicted as a Burmese Python in the film) and subsequently making the glass vanish. In another difference from the book, the glass then reappears, trapping Dudley inside the enclosure.
- The LEGO Harry Potter game titles allow unlimited use of certain basic magic in certain instances even when Harry is in the Muggle world.
- In Hogwarts Mystery, Year 2, chapter 1, Jacob's sibling has the option to tell Rowan Khanna that they practised the spells they had learned before during the 1985 Summer holidays.
- Harry Potter and the Philosopher's Stone (First appearance)
- Harry Potter and the Philosopher's Stone (film)
- Harry Potter and the Chamber of Secrets (Mentioned only)
- Harry Potter and the Chamber of Secrets (film) (Mentioned only)
- Harry Potter and the Prisoner of Azkaban
- Harry Potter and the Prisoner of Azkaban (film)
- Harry Potter and the Order of the Phoenix
- Harry Potter and the Order of the Phoenix (film)
- Harry Potter and the Order of the Phoenix (video game)
- Harry Potter and the Half-Blood Prince (Mentioned only)
- Harry Potter and the Half-Blood Prince (film)
- Harry Potter and the Deathly Hallows
- LEGO Harry Potter: Years 1-4
- LEGO Harry Potter: Years 5-7
- Harry Potter: The Character Vault
- Wizarding World
- Harry Potter: Hogwarts Mystery (Possible appearance) (Mentioned only)
Notes and references
- Harry Potter and the Deathly Hallows, Chapter 11 (The Bribe)
- Harry Potter and the Deathly Hallows, Chapter 18 (The Life and Lies of Albus Dumbledore)
- Harry Potter and the Deathly Hallows, Chapter 33 (The Prince's Tale)
- Harry Potter and the Philosopher's Stone, Chapter 7 (The Sorting Hat)
- Harry Potter and the Philosopher's Stone, Chapter 2 (The Vanishing Glass)
- Harry Potter and the Prisoner of Azkaban, Chapter 2 (Aunt Marge's Big Mistake)
- Writing by J.K. Rowling: "The Quill of Acceptance and The Book of Admittance" at Wizarding World
- Harry Potter: Hogwarts Mystery, Year 7, Chapter 2 (More Questions Than Answers)
- Harry Potter and the Half-Blood Prince, Chapter 13 (The Secret Riddle)
- Writing by J.K. Rowling: "Professor McGonagall" at Wizarding World
- Harry Potter and the Order of the Phoenix
- Harry Potter and the Half-Blood Prince, Chapter 4 (Horace Slughorn)
- Writing by J.K. Rowling: "Ilvermorny School of Witchcraft and Wizardry" at Wizarding World
- Harry Potter and the Chamber of Secrets, Chapter 2 (Dobby's Warning)
- F.A.Q at J. K. Rowling's official site
- Harry Potter and the Philosopher's Stone, Chapter 6 (The Journey from Platform Nine and Three-Quarters)
- Harry Potter and the Goblet of Fire, Chapter 7 (Bagman and Crouch)
- Harry Potter and the Deathly Hallows, Chapter 10 (Kreacher's Tale)
- Harry Potter and the Goblet of Fire, Chapter 9 (The Dark Mark)
- Harry Potter and the Deathly Hallows, Chapter 6 (The Ghoul in Pyjamas)
- Harry Potter and the Chamber of Secrets, Chapter 9 (The Writing on the Wall)
- Harry Potter and the Order of the Phoenix, Chapter 2 (A Peck of Owls)
- Harry Potter and the Order of the Phoenix, Chapter 1 (Dudley Demented)
- Harry Potter: Hogwarts Mystery Year 4, The Trouble with Tonks