Year 2003 (MMIII) was a common year of the Gregorian calendar that started on a Wednesday. 1 episode is in 2001 hiatus. The creators needed time for film production. Gary Takes a Bath is the only episode that premiered in the Summer of 2003.
- January 1: The Amazing SpongeBobini was released.
- January 5: Clancy Brown's 44th birthday
- January 8: David Bowie's 46th birthday
- January 13: Charles Nelson Reilly's 72nd birthday
- January 15:
- Andrea Martin's 56th birthday
- The Australian release of SuperSponge became one year old.
- January 17: Sleepy Time and Suds became three years old.
- January 22: Jim Jarmusch's 50th birthday
- January 24:
- Ernest Borgnine's 86th birthday
- The Great Snail Race and Mid-Life Crustacean premiered.
- January 25: Christopher Ryan's 53rd birthday
- January 27: Patton Oswalt's 34th birthday
- February 5:
- Christopher Guest's 55th birthday
- Robin Sachs's 52nd birthday
- February 13: Carolyn Lawrence's 36th birthday
- February 14: Valentine's Day and The Paper became three years old.
- February 17: Wormy and Patty Hype became two years old.
- February 22:
- Nigel Planer's 49th birthday
- Snowball Effect and One Krab's Trash became one year old.
- March 1: Nasty Patty and Idiot Box became one year old.
- March 2: Laraine Newman's 51st birthday
- March 4: Lost at Sea was released.
- March 5: Survival of the Idiots and Dumped became two years old.
- March 6:
- Eddie Deezen's 46th birthday
- Grandma's Kisses and Squidville became two years old.
- March 7:
- Rik Mayall's 45th birthday
- No Free Rides and I'm Your Biggest Fanatic became two years old.
- March 8:
- Pressure and The Smoking Peanut became two years old.
- As Seen on TV and Can You Spare a Dime? became one year old.
- March 9: Shanghaied became two years old.
- March 10: Shannon Tweed's 46th birthday
- March 11: Johnny Knoxville's 32nd birthday
- March 12: Nautical Nonsense and Sponge Buddies became one year old.
- March 14:
- Legend of the Lost Spatula became two years old.
- Revenge of the Flying Dutchman was released on Playstation 2 in Europe.
- March 15:
- Dee Snider's 49th birthday
- Arrgh! and Rock Bottom became three years old.
- No Weenies Allowed and Squilliam Returns became one year old.
- March 21: The Sponge Who Could Fly premiered.
- March 22:
- Texas and Walking Small became three years old.
- The Algae's Always Greener and SpongeGuard on Duty became one year old.
- March 25: Gene Shalit's 78th birthday
- March 28: Revenge of the Flying Dutchman was released on Game Boy Advance and GameCube in Europe.
- March 29:
- Amy Sedaris' 42nd birthday
- Krab Borg and Rock-a-Bye Bivalve became one year old.
- April 1; Fools in April and Neptune's Spatula became three years old.
- April 2:
- Martin Olson's 50th birthday
- Nicktoons Battle became one year old.
- April 3:
- Alec Baldwin's 47th birthday
- Alton Brown's 41st birthday
- Sebastian Bach's 35th birthday
- April 8:
- Biz Markie's 39th birthday
- Hooky and Mermaid Man and Barnacle Boy II became three years old.
- April 9: Dennis Quaid's 50th birthday
- April 11: Jimmy Neutron's Nicktoon Blast opened.
- April 16: Billy West's 53rd birthday
- April 17: Victoria Beckham's 30th birthday
- May 1:
- SpongeBob SquarePants became four years old.
- Help Wanted, Reef Blower, and Tea at the Treedome became four years old.
- May 2: Matt Berry's 33rd birthday
- May 5:
- John Rhys-Davies's 55th birthday
- Pre-Hibernation Week and Life of Crime became two years old.
- May 9:Rosario Dawson's 24th birthday
- May 10: Wet Painters and Krusty Krab Training Video became one year old.
- May 17:
- Craig Ferguson's 41st birthday
- Party Pooper Pants became one year old.
- May 18: Tina Fey's 33rd birthday
- May 22: Ginnifer Goodwin's 25th birthday
- May 31: Chris Elliot's 43rd birthday
- June 1:
- Chocolate with Nuts and Mermaid Man and Barnacle Boy V became one year old.
- Hands Off! was released.
- June 9: Johnny Depp's 40th birthday
- June 12: Junior Brown's 51st birthday
- June 20: John Goodman's 51st birthday
- June 25: Ricky Gervais's 41st birthday
- June 28: Pat Morita's 71st birthday
- July 6: Burt Ward's 58th birthday
- July 12: Club SpongeBob and My Pretty Seahorse became one year old.
- July 13: Tom Kenny's 43rd birthday
- July 14: SpongeBob SquarePants's 17th birthday
- July 16: Will Ferrell's 36th birthday
- July 17:
- David Hasselhoff's 51st birthday
- Bubblestand and Ripped Pants became four years old.
- July 18: Lori Alan's 37th birthday
- July 21: Robin Williams's 44th birthday
- July 26: Gary Takes a Bath premiered.
- July 29: Tide and Seek was released.
- July 30: Jim Wise's 39th birthday
- July 31: Jellyfishing and Plankton! became four years old.
- August 7: Naughty Nautical Neighbors and Boating School became four years old.
- August 10: Antonio Bandaras' 43rd birthday
- August 13: The European release of SuperSponge became two years old.
- August 14: Pizza Delivery and Home Sweet Pineapple became four years old.
- August 16: Stew's 42nd birthday
- August 18: Andy Samberg's 25th birthday
- August 21:
- Stephen Hillenburg's 42nd birthday
- Mermaid Man and Barnacle Boy and Pickles became four years old.
- August 22: Kristen Wiig's 30th birthday
- August 25: Gene Simmons's 51st birthday
- [[August 26]}: Nicktoons Halloween was released.
- August 27: The Halloween DVD and VHS became one year old.
- August 28: Hall Monitor and Jellyfish Jam became four years old.
- September 2: Mary Jo Catlett's 65th birthday
- September 4:
- John DiMaggio's 35th birthday
- Sandy's Rocket and Squeaky Boots became four years old.
- September 5: David Glen Eisley's 51st birthday
- September 6: Graveyard Shift and Krusty Love became one year old.
- September 7: The Secret Box and Band Geeks became two years old.
- September 8: P!nk's 24th birthday
- September 9: Corky Carroll's 56th birthday
- September 10:
- September 11: Nature Pants and Opposite Day became four years old.
- September 16:
- Amy Poehler's 32nd birthday
- Krusty Krab Adventures was released.
- September 18:
- Culture Shock and F.U.N. became four years old.
- The Game Boy Color version of Nicktoons Racing became four years old.
- September 19: Adam West's 75th birthday
- September 20: New Student Starfish and Clams became one year old.
- September 21: Sailor Mouth and Artist Unknown became two years old.
- September 22: The Employee of the Month game became one year old.
- September 24: Operation Krabby Patty became two years old.
- September 25:
- Mark Hamill's 52nd birthday
- MuscleBob BuffPants and Squidward the Unfriendly Ghost became four years old.
- September 26: Sirena Irwin's 26th birthday
- September 28: Jellyfish Hunter and The Fry Cook Games became two years old.
- September 29: Ian McShane's 61st birthday
- September 30: Christmas and Nicktoons Christmas were released.
- October 2: The Chaperone and Employee of the Month became four years old.
- October 4:
- Bill Fagerbakke's 46th birthday
- Born Again Krabs and I Had an Accident premiered.
- October 5: Just One Bite and The Bully became two years old.
- October 9: John O'Hurley's 50th birthday
- October 12: Squid on Strike and Sandy, SpongeBob, and the Worm became two years old.
- October 15: Nickelodeon Toon Twister 3-D was released.
- October 17: Michael McKean's 55th birthday
- October 21:
- Lux Interior's 56th birthday
- Battle for Bikini Bottom was released.
- October 25: Kevin Michael Richardson's 37th birthday
- October 26: Something Smells and Bossy Boots became three years old.
- October 28: Scaredy Pants and I Was a Teenage Gary became four years old.
- October 30: The North American Xbox release of Nickelodeon Party Blast became one year old.
- October 31:
- Brian Doyle-Murray's 58th birthday
- The PC version of Nicktoons Racing became three years old.
- The PC version of Nickelodeon Party Blast became one year old.
- November 1: Daran Norris's 39th birthday
- November 2: Your Shoe's Untied and Squid's Day Off became three years old.
- November 5:
- The United States release of SuperSponge became two years old.
- Shanghaied: Patrick's ending and Shanghaied: Squidward's ending became one year old.
- Sea Stories became one year old.
- November 11: Friends Forever was released.
- November 16: Big Pink Loser and Bubble Buddy became three years old.
- November 18: Rich Fulcher's 35th birthday
- November 20: Rodger Bumpass' 52nd birthday
- November 21: The United States Playstation 2 release of Revenge of the Flying Dutchman became one year old.
- November 22: Scarlett Johansson's 19th birthday
- November 27: Grandma's Kisses, Squidville, Mermaid Man and Barnacle Boy III, and Squirrel Jokes became three years old.
- November 30:
- Eugene H. Krabs and Sheldon J. Plankton's 61st birthday
- Procrastination and I'm with Stupid became two year old.
- December 4: A Chuckie Finster Christmas, Channukah, Kwaanza, Winter Solstice, Holiday Party, How The You-Know-Who Stole You-Know-What!, Patrick the Snowman, Plankton's Holiday Hits, and The 12 Days of Nickmas became one year old.
- December 6:
- Christmas Who? became three years old.
- The GameCube and PAL region Xbox releases of Nickelodeon Party Blast became one year old.
- December 14: John Lurie's 37th birthday
- December 15:
- Tim Conway's 70th birthday
- Rodney Bingenheimer's 56th birthday
- December 18:
- Ray Liotta's 50th birthday
- The United States GameCube release of Revenge of the Flying Dutchman became one year old.
- December 19: Jill Talley's 42nd birthday
- December 25: Bikini Bottom's fifth Christmas
- December 28: Dying for Pie and Imitation Krabs became three years old.
- December 30:
- Davy Jones' 58th birthday
- LeBron James's 19th birthday
- December 31: SB-129 and Karate Choppers became four years old.