Past Tense of “speed”
The past tense of speed is sped; the past participle is sped.
Why “speed” behaves this way
"Speed" comes from Old English "spedan," related to the noun "sped" meaning success or prosperity — the same root survives in the old blessing "godspeed," literally wishing someone good success or good fortune on their journey, not merely a fast trip. The verb's original sense was "to succeed" or "to prosper," and only later, through the notion of a journey succeeding quickly and efficiently, did the meaning narrow to today's sense of moving fast.
The irregular past form "sped" is a dental-preterite survival from this older weak-verb pattern with vowel shortening, the same mechanical process that produced "keep/kept" and "sleep/slept." But because the meaning of "speed" split into two distinct senses in modern English — moving fast, and specifically exceeding a legal speed limit — the verb has effectively developed two different past-tense behaviors depending on which sense is intended, something most irregular verbs on this list don't have to contend with. This sense-splitting conjugation is a relatively recent development tied directly to the rise of automobile traffic law in the twentieth century; before cars existed, there was no legal-violation sense of "speed" to prompt a competing regularized form in the first place.
The common confusion
The genuine modern split is this: "sped" is used for the general sense of moving quickly ("she sped down the hallway"), while "speeded" survives specifically in the legal or driving-violation sense, especially in the fixed phrasal form "speeded up" and in British legal writing ("he was speeding and was later found to have speeded on three previous occasions"). American English tends to use "sped up" for the phrasal sense as well, narrowing the gap between the two forms compared to British usage. Dictionaries themselves aren't fully consistent about labeling this split, with some listing "speeded" as simply a variant of "sped" without noting the meaning-based distinction, which leaves many writers to pick up the actual usage pattern from reading rather than from any single reference source.
How it's actually used
Because of this sense-based split, careful writers choose between "sped" and "speeded" based on meaning rather than dialect alone: "the car sped down the street" describes ordinary rapid motion, while "production speeded up considerably" (or "sped up," in American usage) describes an increase in a rate or process, a usage that behaves almost like a distinct phrasal verb with its own preferred conjugation. News writing about traffic incidents and legal proceedings tends to favor whichever form matches the surrounding dialect of the publication rather than any universal rule, so British court reporting and American traffic reporting can genuinely differ in which form reads as the default, unmarked choice for the exact same underlying event.
Across the tense system
In the perfect tense, "has sped" is standard for describing general fast movement ("the ambulance has sped to dozens of emergencies this year"), while "has speeded up" or "has sped up" both appear in writing about processes and rates, with "sped up" now dominant in American English and both forms still competing in British English.
Common real mistakes
The clearest real error is using "speeded" for the general motion sense where "sped" is expected ("he speeded down the highway" instead of the more natural "he sped down the highway"), a mistake that isn't strictly ungrammatical but reads as noticeably less idiomatic to most native ears. A second, opposite error is using "sped" where the legal or fixed-phrase sense specifically calls for "speeded," particularly in older British legal documents that maintain "speeded" as the standard term for a driving violation. A third, more subtle error shows up in tech and business writing about accelerating a process, where some writers alternate unpredictably between "sped up" and "speeded up" within the same document rather than settling on one consistent choice, an inconsistency that reads as sloppy even though both forms are independently defensible depending on the register.
Examples
- The ambulance sped through the intersection.
- Production has sped up significantly since the new equipment arrived.
- He sped away before anyone could get his license plate.
- The rumor sped through the office within minutes.
- They had sped past the checkpoint without stopping.
- The train sped along the coast at nearly two hundred miles an hour.
Memory trick
Let the meaning guide the form: think "sped" for the everyday, physical sense of moving fast (like "fled" or "bled"), and reserve "speeded up" mentally for the specific sense of a rate or process increasing, especially in older or British writing.