life long

Short answer: write lifelong as one word when you mean "lasting throughout life."

Quick answer

Use lifelong (closed) to mean "lasting the whole of a life." Avoid the two-word life long. The hyphenated life-long is uncommon and usually unnecessary unless a specific style guide requires it.

As an adjective: a lifelong friend, lifelong learning, lifelong commitment.
When you need a noun form, use lifetime: a lifetime achievement, a lifetime warranty.
If unsure, prefer lifelong - it's the standard form in most dictionaries and style guides.

Core explanation: closed compounds, spacing, and hyphens

When "long" follows a noun to indicate duration, English typically forms a closed compound: lifelong, yearlong, daylong. That means no space and, in most cases, no hyphen.

Write life long (two words) only if you truly mean the noun "life" followed by a separate adjective "long" - a rare structure. Use life-long with a hyphen only for consistent house-style reasons or to avoid confusion in a complex modifier.

Pattern: noun + long → closed compound for duration (life + long → lifelong).
Test: can you replace it with "for the rest of [someone's] life" or "a lifetime of"? If yes, use lifelong.
Hyphen rule: default to lifelong; hyphenate only if required by style or readability in stacked modifiers.

Grammar: part of speech and common constructions

Lifelong is primarily an adjective modifying nouns: lifelong friend, lifelong career, lifelong learner. It rarely acts as a noun or adverb. Use lifetime when you need a noun or a clearer compound adjective in legal or formal phrasing.

Adjective (correct): lifelong commitment.
Noun (use lifetime): a lifetime warranty.
Adverb (avoid): not "He lifelong studies law" - write "He is a lifelong student of law" or "He studies law throughout his life."

Real usage and tone: formal, academic, casual

Lifelong fits formal, academic, and casual contexts. For legal precision or emphasis, pick lifetime or explicit phrasing like "for the lifetime of the product" or "for the rest of their life."

Formal/professional: lifelong commitment, lifelong partnership.
Academic: lifelong learning is a standard phrase in education research.
Casual: lifelong friend, lifelong dream - perfectly natural in conversation.

Examples bank: wrong/right pairs you can copy

Below are concise wrong/right pairs grouped by context. Copy the "Right" sentence where it fits.

Work - Wrong: We need a life long strategy for customer retention.Work -
Right: We need a lifelong strategy for customer retention.
Work - Wrong: They signed a life long contract with the supplier.Work -
Right: They signed a lifelong contract with the supplier.
Work - Wrong: The department is committed to life long diversity initiatives.Work -
Right: The department is committed to lifelong diversity initiatives.
School - Wrong: He is a life long learner who takes extra classes every semester.School -
Right: He is a lifelong learner who takes extra classes every semester.
School - Wrong: Her life long interest in chemistry drove her to graduate school.School -
Right: Her lifelong interest in chemistry drove her to graduate school.
School - Wrong: The study examined life long learning outcomes.School -
Right: The study examined lifelong learning outcomes.
Casual - Wrong: I'm looking for a life long partner who shares my values.Casual -
Right: I'm looking for a lifelong partner who shares my values.
Casual - Wrong: My dad had a life long love of fishing.Casual -
Right: My dad had a lifelong love of fishing.
Casual - Wrong: She told me about her life long dream to travel the world.Casual -
Right: She told me about her lifelong dream to travel the world.

Rewrite help: fix your sentence in three quick steps

1. Spot - Search your text for "life long" and "life-long."
2. Decide - If the phrase modifies a noun to mean "throughout life," replace it with lifelong.
3. Polish - If the result feels awkward, rephrase using "for the rest of their life" or "a lifetime of."

Work - Rewrite:
Original: "We signed a life long partnership." → Simple fix: "We signed a lifelong partnership." → Stronger: "We entered a partnership intended to last a lifetime."
School - Rewrite:
Original: "She has a life long interest in art." → Simple fix: "She has a lifelong interest in art." →
Alternative: "She has been interested in art her whole life."
Career - Rewrite: Original: "He is looking for a life long career in finance." → Simple fix: "He is looking for a lifelong career in finance." →
Alternative: "He hopes to build a career in finance that spans his working life."

Memory trick and quick checklist

Mnemonic: If it describes a whole life, stick it together - lifelong.

Find: search for "life long" or "life-long."
Test: does it mean "lasting a lifetime"? If yes, use lifelong.
Replace or rephrase: lifelong or "for the rest of their life" / "a lifetime of."
Read aloud to check flow.

Similar mistakes to watch for

The same pattern applies to other duration compounds. Close them up when they mean duration; hyphenate only where standard usage demands it.

Correct: lifetime, yearlong, daylong. Common hyphenation: day-to-day, all-time (varies by use).
Wrong spacing: life time → lifetime; year long → yearlong.
Wrong: She wanted a life time warranty on the product.
Right: She wanted a lifetime warranty on the product.
Wrong: He opened a year long savings account.
Right: He opened a yearlong savings account.
Wrong: This is an all time favorite song (as modifier).
Right: This is an all-time favorite song.

FAQ

Is it life long or lifelong?

Write lifelong as one word when you mean "lasting a lifetime." Life long (two words) is incorrect for that meaning.

Should I use life-long with a hyphen?

No - most dictionaries and style guides prefer lifelong without a hyphen. Reserve life-long only for strict house-style rules or rare clarity cases.

Can I say "lifetime" instead?

Yes. Lifetime functions as a noun or adjective (a lifetime achievement, a lifetime warranty). Choose lifetime when the noun form reads better.

Is lifelong acceptable in academic writing?

Yes. Phrases like "lifelong learning" are standard and widely accepted in academic and professional writing.

Quick fix: how do I change my sentence?

If your sentence uses life long or life-long to mean "lasting a lifetime," replace it with lifelong. If it still sounds awkward, rewrite with "for the rest of their life" or "a lifetime of."

Want help fixing a sentence?

Paste a sentence into a grammar tool to catch spacing and hyphenation. Tools will flag life long and suggest lifelong so you can fix it fast. For team consistency, standardize on lifelong (closed) across documents.