accelerate

Writers often swap accelerate and speed up without checking meaning or audience. Below are clear rules, tight rewrites, hyphenation and grammar notes, plus many copy-and-paste examples you can use immediately.

Focus on two signals: whether you mean a measured change in rate (use accelerate) or a plain instruction/outcome (use speed up or a clearer verb).

Quick answer

Use accelerate when reporting a measured change in rate or velocity (with units or formulas). Use speed up for instructions, user-facing text, and most workplace prose. When unsure, name the agent and the measurable outcome.

Prefer speed up for documentation, help text, and action items.
Use accelerate in physics/engineering or when you report a continuous, measured change (e.g., "accelerated at 3 m/s²").
If either word makes the sentence vague, rewrite to name the agent or use a precise noun: "increase the rate," "reduce latency," or "expedite the process."

Core difference: meaning and nuance

Accelerate emphasizes a change in rate/velocity and fits measured, continuous processes. Speed up is a direct phrasal verb meaning "make faster" or "become faster," and reads clearer for instructions and everyday writing.

accelerate = change in rate/velocity (measured, often continuous).
speed up = make faster / become faster (plain, action-focused).

Hyphenation and spacing (speed up, speed-up, speedup)

Keep these forms straight:

Verb phrase: speed up (two words). Example: "Speed up the build."
Compound adjective before a noun: speed-up (hyphen). Example: "A speed-up in parsing saved 10 ms."
Noun form: speed-up or speedup. Prefer speed-up in formal writing; speedup is common in notes and technical contexts.

Grammar notes: transitivity, separable phrasal verb, and agents

Both verbs can be transitive or intransitive: "The engine accelerated" (intransitive) vs "The driver accelerated the car" (transitive).

"Speed up" can split the object-"speed the process up"-but "speed up the process" is usually clearer.
Always name the agent and quantify the result when it matters: "The update sped up response times by 25%," not "The system accelerated."
If you mean "increase rate" rather than change velocity, consider "increase the rate," "reduce latency," or "expedite."

Real usage and tone: match word to audience

Pick the word that fits reader expectations:

Technical paper or lab report → accelerate when you report measured acceleration or rates with units.
User docs, product copy, emails → speed up for clarity and actionability.
Marketing → avoid vague "accelerate"; give concrete metrics or benefits instead.

Technical: "The vehicle accelerated at 1.5 m/s² during the test."
User doc: "To speed up the app, clear the cache and restart."
Marketing (rewrite): Instead of "We accelerated onboarding," say "We cut onboarding time from 10 to 4 minutes."

Side-by-side: wrong → right (copyable rewrites)

Common swaps and tighter rewrites that fix tone, agent, and clarity.

Wrong: We need to accelerate the program.
Right: We need to speed up the program by optimizing the hot loop.
Wrong: The car accelerated quickly.
Right: The car sped up rapidly.
Wrong: To accelerate onboarding, send more emails.
Right: To speed up onboarding, remove unnecessary steps and send one confirmation email.
Wrong: The reaction accelerated after the catalyst was added.
Right: The reaction sped up after we added the catalyst (completion time fell from 60 to 30 minutes).
Wrong: We accelerated sales by changing the pricing page.
Right: We sped up sales growth by simplifying the pricing page and reducing checkout friction.
Wrong: Policy changes will accelerate inflation.
Right: Policy changes will likely speed up inflation (if passed, CPI could rise by X%).
Wrong: Accelerate the pipeline.
Right: Speed up the pipeline by running jobs in parallel and adding caching.
Wrong: The system accelerated after the update.
Right: Performance improved after the update; response times sped up by 25%.

Try your own sentence

Test the whole sentence, not just the phrase. Context reveals whether you mean "make faster," "measured change," or something procedural.

Examples by context: work, school, casual

Choose the phrasing that fits tone and audience.

Work: "To speed up the CI pipeline, enable dependency caching and parallel tests."
Work: "The analytics changes sped up report generation by 40%."
Work (formal): "Vehicle acceleration was measured at 2.1 m/s² during the trial."
School: "The enzyme-catalyzed reaction accelerated at higher temperatures (rate constant k increased)."
School (lab): "The reaction sped up when the catalyst was added; record the time difference."
School (essay): "If you lack velocity data, write 'increase the rate' instead of 'accelerate.'"
Casual: "My commute sped up after they fixed the lights."
Casual: "I sped up to catch the bus."
Casual (rewrite): Instead of "I accelerated my pace walking," say "I sped up my pace."

Rewrite help: fix your sentence in three steps

Three-step edit: (1) Decide whether you mean "make faster" or "measured change." (2) Name the agent and the outcome. (3) Choose speed up or a more precise verb/noun and add a metric.

If you mean "make faster" → use speed up and name the action.
If you report a measured change → accelerate is OK, but include numbers.
If ambiguous → rewrite with "increase the rate," "expedite," or "reduce latency."

Original: "We need to accelerate the onboarding."
Rewrite: "We need to speed up onboarding by removing two steps and adding a progress bar."
Original: "The process accelerated during testing."
Rewrite: "The process sped up during testing, reducing completion time by 20%."
Original: "Accelerate model training."
Rewrite: "Speed up model training by using mixed precision and distributed GPUs."
Original: "We accelerated approval."
Rewrite: "We expedited approval by removing one required signature, cutting turnaround from 3 days to 1."
Original: "Traffic accelerated after 9 AM."
Rewrite: "Traffic flow increased after 9 AM; average speed dropped 12%."

Memory trick and style tips

Replace the verb with "make faster." If the meaning stays the same, use speed up. If you need units or rates, use accelerate.

Heuristic: make faster → speed up; measured rate/velocity → accelerate.
Prefer active verbs and add numbers or agents to remove vagueness.
In instructions, default to speed up; in measurement, use accelerate with a metric.

Similar mistakes: expedite, hasten, boost, increase

Pick the verb that captures agent and mechanism:

Expedite = remove delays or obstacles (procedural). Example: "We expedited approval."
Hasten = cause something to happen sooner (urgency), often editorial or literary.
Boost / Increase = raise magnitude, not necessarily the rate. Use them when you mean "more" rather than "faster."
When precision matters, prefer a short noun phrase: "increase the rate," "reduce latency," "cut completion time."

FAQ

When should I use accelerate instead of speed up?

Use accelerate for measured changes in velocity or rate (physics, engineering, or data with units). For instructions, documentation, and most workplace sentences, speed up reads clearer.

Is "speedup" one word or two?

As a verb phrase it's two words: speed up. As a noun, usage varies: speed-up (hyphen) is preferred in formal writing; speedup is common in informal or technical notes.

Can I use accelerate in product copy or marketing?

You can, but "accelerate" often feels vague. Prefer concrete claims: replace "accelerate onboarding" with "cut onboarding time from 10 to 4 minutes."

How do I fix "accelerate" sentences quickly in a draft?

Ask: Do I mean "make faster" or "measured change"? Who is the agent? What result matters? Then swap to speed up and name the action, or rewrite with "increase the rate," "expedite," or a specific metric.

When should I hyphenate "speed up"?

Don't hyphenate when it's a verb phrase ("speed up the server"). Hyphenate when it modifies a noun: "a speed-up in processing." For technical nouns, "speedup" is also common.

Want a quick check on a sentence?

Paste one line and get a short rewrite that fits your audience (user doc, report, or email). Focus edits on naming the agent and adding a metric where possible.