A project manager sends over a 20,000-word technical manual for light post-editing. “Just make it readable,” the brief says. You open the file and the MT output is rough - passive constructions stacked on passive constructions, safety warnings that read “operate near the heating element” where the source says “do not operate near the heating element,” product names transliterated into something unrecognizable. Three hours in, you’ve reworked 2,000 words and you’re nowhere near “readable.”
That’s the light vs. full post-editing problem in one example. Wrong classification plus wrong rate equals you lose money, the client gets unhappy, and the project runs late.
Here’s the framework for getting this right before you start.
What ISO 18587 actually defines¶
ISO 18587:2017 is the international standard for post-editing of machine translation output. It’s the closest thing the industry has to a universal definition of LAPE and FAPE - and understanding what it says is the foundation for any serious conversation about PE scope and pricing.
Light post-editing (LAPE) per ISO 18587 means “limiting corrections to the most serious errors so that the text is understandable.” The goal is comprehension, not quality. The output doesn’t have to be stylistically polished, terminologically consistent, or natural-sounding - it just has to convey the meaning accurately enough that a reader understands it.
Full post-editing (FAPE) means “producing a result comparable to professional human translation.” That’s a much higher bar - the output must be accurate, terminologically correct, stylistically appropriate for the target audience, grammatically sound, and consistent throughout.
The standard puts it this way:
Full post-editing aims to produce output that meets the same quality requirements as professional human translation, including accuracy, terminology, linguistic quality, style, and format.
This distinction matters more than most clients realize. Full PE isn’t “post-editing done carefully.” It’s a professional translation service where AI does the first pass and a qualified translator does everything else a human translator would do. The MT draft is a drafting tool, not a substitute for the translator’s judgment.
The standard also defines qualification requirements for post-editors. Full PE requires the same competencies as a professional translator: translation competence, research skills, subject-matter expertise, and understanding of MT systems and their limitations. Light PE has slightly relaxed requirements, but it still demands genuine language expertise - not just bilingualism.
This is relevant when clients ask whether their bilingual intern can “quickly review” an MT output at light PE rates. The answer is no - light PE is a professional service even if it’s scoped more narrowly than full PE.
What the difference looks like in actual output¶
The standard definitions are clean on paper. In practice, the difference shows up in what you actually do - and don’t do - to the text.
In light post-editing, you’re running through the text asking one question: does this sentence convey the correct meaning in a way the reader can understand? If yes - move on, even if it’s awkward. What you don’t fix: - Unnatural word order or phrasing that doesn’t affect comprehension - Inconsistent terminology (unless it creates genuine confusion) - Style that doesn’t match the client’s brand voice - Minor grammar issues that don’t change meaning - Register mismatches (formal vs. informal) that aren’t jarring enough to confuse
In full post-editing, you’re asking the same question plus: would a professional translator have written it this way? What you fix: - Everything in the light PE list above - Terminology against approved glossaries or client style guides - Register and tone appropriate for the target audience - Format and structure matching target-language conventions - Completeness - nothing omitted, nothing added that wasn’t in the source - Consistency throughout the document
Here’s the same sentence at both levels:
Source (German): “Das Gerät darf nicht in Betrieb genommen werden, bevor alle Sicherheitsüberprüfungen abgeschlossen sind.”
MT output: “The device may not be commissioned before all safety checks have been completed.”
Light PE result: “Do not commission the device before all safety checks are completed.” - Fixes the critical meaning error (“may not” vs. “do not”), leaves the rest.
Full PE result: “The device must not be put into operation until all safety inspections have been completed and recorded.” - Fixes meaning, adjusts register for technical documentation, matches industry-standard phrasing (“put into operation” instead of “commissioned” for the target audience), ensures the action requirement is explicit.
One targeted edit for comprehension. Multiple coordinated edits for publication quality.
The practical implication: if you’re doing light PE correctly, you’re moving fast and leaving a lot on the table intentionally. If you find yourself fixing style, terminology consistency, and register issues - you’ve crossed into full PE territory, whether the brief says so or not.
The five-factor decision framework¶
No single rule covers every case. But these five questions get you to the right answer for almost every project - and if you use them consistently before starting work, you avoid the misclassification problem.
1. Who reads it?¶
Internal audience (your own team, internal SMEs, people with context) - light PE is usually appropriate. They know the subject matter, they understand what the document is for, and they’ll catch issues a general reader wouldn’t.
External audience (customers, regulators, courts, the public, business partners you want to impress) - full PE, no exceptions. Your brand, your credibility, and in some domains your legal exposure are on the line as soon as the content leaves your organization.
A middle case: a translation that goes to internal reviewers who then send it to external parties. This is effectively external - treat it as full PE.
2. Where does it go?¶
Into an internal inbox or shared drive for reference - light PE. Into a product manual, regulatory filing, published website, contract, court submission, or anything that will be seen by people outside the organization - full PE.
The destination determines the stakes. A translation that lives in an internal wiki can be imperfect. A translation filed with a regulator, published in a product, or submitted to a court cannot. If you’re unsure where the content will end up, ask before you start - not after.
3. How long does it live?¶
One-time gist translation that will be read once, used for a specific decision, and then archived or discarded - light PE makes sense. Content that will be archived, cited, used as a reference for months or years, translated into additional languages, or republished - full PE.
Short-lived content with low stakes is ideal for light PE. Long-lived content with any ongoing use should be full PE, because the cost of errors compounds over time. A terminology inconsistency in a document that gets used as a template for 50 future documents is a much bigger problem than a terminology inconsistency in a document that nobody ever opens again.
4. What domain is it in?¶
General business content, meeting summaries, internal reports, casual communications - light PE can work if the other factors support it.
Legal, medical, pharmaceutical, regulatory, financial, or technical (machinery, safety systems, engineering) - full PE only. The terminology precision in these domains is non-negotiable, and a terminology error isn’t just embarrassing. In legal and medical contexts, it can be expensive or dangerous.
As our article on AI hallucinations in legal translation covers in detail, the most dangerous translation errors are the ones that look correct - dropped negations, subtle meaning shifts, added specificity that wasn’t in the source. Light PE isn’t designed to catch these because it’s designed to be fast, not thorough.
5. What happens when there’s an error?¶
If the cost of an error is “reader confusion that gets resolved by a follow-up email” - light PE tolerance is reasonable.
If the cost is “product recall,” “regulatory fine,” “contract dispute,” “patient harm,” “failed audit,” or “lost deal” - full PE is the only defensible choice.
This is the override factor: even if all four previous factors suggest light PE might work, the answer to factor #5 can flip the decision alone. Document type and destination matter less than consequences. A low-stakes internal document for a high-stakes decision is still a high-stakes translation.
Project type decision matrix¶
| Project type | PE level | Reasoning |
|---|---|---|
| Internal reports, memos, meeting notes | Light | Internal audience, comprehension is the goal |
| Research summaries for internal use | Light | Gist only, SMEs interpret the content |
| Customer emails, support responses | Full | External audience, brand visible |
| Technical manuals (external) | Full | Safety, liability, regulatory requirements |
| Technical manuals (internal only) | Case-by-case | Depends on safety criticality |
| Legal documents (contracts, filings) | Full | Legal liability, terminology precision |
| Medical and pharmaceutical content | Full | Patient safety, regulatory compliance |
| Marketing copy, website content | Full or Human-only | Brand, creative quality, tone of voice |
| Software UI, localization strings | Full | UX depends on precise phrasing |
| Press releases | Full | Public-facing, brand-critical |
| Financial reports (regulatory filings) | Full | Compliance, audit requirements |
| Academic papers (for publication) | Full | Peer-review standards |
| Employee handbook (internal reference) | Light | Internal, non-binding, reference use |
| Patent applications | Full | Legal precision, jurisdiction-specific requirements |
| Training materials (internal) | Light | Internal, comprehension-focused |
| Training materials (external/certifying) | Full | External, quality expectations, liability |
One note on marketing and creative content: full PE is often the minimum, but many brand-critical campaigns and creative assets do better with human-only translation or transcreation. MT produces safe, grammatically correct output - which is fine for instructional content but typically kills creative impact. If the brief asks for “natural-sounding” or “on-brand” output for marketing, that’s a conversation about whether MT should be involved at all.
A practical question to ask for any ambiguous case: “Would I be comfortable if the client’s CEO read this and asked who translated it?” If yes - your PE level is probably right. If no - you need either full PE or human-only.
Rates and how to quote MTPE work¶
This is where MTPE engagements most often go wrong. The rate conversation has to happen before the project starts, based on the agreed PE level - not negotiated after the fact.
Current market rates for 2024-2025:
| Service | Rate per word | Speed | Daily output (8h) |
|---|---|---|---|
| Human translation | $0.15-0.30 | 200-300 words/hour | ~2,000 words |
| Full post-editing | $0.08-0.15 | ~700 words/hour | ~5,600 words |
| Light post-editing | $0.02-0.05 | ~1,000 words/hour | ~8,000 words |
A few important caveats about these numbers.
First, research from Slator shows that productivity varies enormously by language pair. English-to-French MTPE can run 130% faster than human translation. Some language combinations - particularly those with greater structural distance - show almost no speed advantage at all. English-to-Swedish in one study was actually 7% slower than human translation alone. The numbers above are averages across favorable conditions, not guarantees.
Second, about half of professional translators don’t offer discounts for MTPE work. A 2025 survey of 212 freelance translators found that approximately 50% resist per-word rate cuts for post-editing, arguing that poor MT output can require effort comparable to translating from scratch - and they’re right. When the MT quality is poor, you’re not editing a draft. You’re translating with extra friction.
Third - and this is the rule that prevents most rate disputes - always run a diagnostic sample before committing to per-word rates on a large volume. Take 300-500 words, work through them carefully, time yourself, and calculate your effective hourly rate. If it comes out below your minimum acceptable rate, the per-word price isn’t right. This is the only reliable way to quote MTPE: test the specific MT engine, language pair, and domain you’ll actually be working with.
The question clients often ask: “Why does post-editing cost anything if the AI already translated it?” The answer is concrete: you’re reviewing every sentence for meaning accuracy, catching critical errors the MT introduced, and taking professional responsibility for the output. The AI isn’t liable when something goes wrong. You are.
One workflow that addresses this clearly: platforms like ChatsControl route AI-generated translation to qualified sworn translators for full review and certification - essentially implementing the full PE model as a managed service. It’s a useful reference when clients ask whether an AI output “should be good enough” without human review.
The misclassification trap¶
The most expensive mistake in MTPE isn’t choosing the wrong per-word rate. It’s accepting the wrong project scope.
Here’s how it happens: a client briefs “light PE.” You take the job. You open the file and realize the content is highly technical, the MT quality is low, and the target audience is external customers or regulators. To do this job responsibly, you need to do full PE work. But you’re contracted for light PE rates.
A 2025 survey of 212 professional translators found that 66% report MTPE output requires “significant edits” even after MT processing. That number suggests a substantial portion of “light PE” briefs in the market are actually full PE jobs in disguise. Clients don’t always understand the distinction - and some exploit the ambiguity intentionally.
How to protect yourself:
Define scope in writing before you start. Your contract or purchase order should specify the PE level explicitly, with reference to ISO 18587 LAPE or FAPE. “Post-editing” without qualification is meaningless. So is “light editing” or “quick review” - these aren’t standard terms with agreed definitions.
Run a diagnostic sample first. Before committing to a large project at light PE rates, review 300-500 words and document what you find: how many error types appear? Are there meaning shifts, omissions, added content that wasn’t in the source? Structural errors that require complete rewriting? This gives you evidence if the scope needs to change.
Build in an escalation clause. Define what triggers a reclassification: for example, if more than X% of segments require structural revision, or if the per-segment edit time exceeds Y minutes, the work reclassifies as full PE at the full PE rate. Put this in writing, not as a verbal agreement.
Communicate early, not after. If you’re 20% into a job and realize it’s been misclassified, stop and contact the PM with specific examples. “This section alone required complete rewriting because the MT dropped two negations and added a liability clause that wasn’t in the source - this is full PE work” is a conversation that PMs can act on. “I spent too much time on this” after the fact is not.
Know when to decline. If a client insists on light PE rates for content that clearly requires full PE - legal documents, technical manuals for external use, medical content - declining is the right call. You can’t do a responsible job at light PE scope on content that requires full PE attention, and if something goes wrong, you’re the professional who signed off on it.
How to brief clients correctly¶
Most clients who misclassify PE scope aren’t trying to exploit you - they genuinely don’t understand the difference. Part of your job is educating them before problems occur.
When a client asks for “post-editing” without specifying the level, don’t assume light PE because it’s cheaper. Ask:
- “Who is the target audience for this content?”
- “Where will it be published or used?”
- “What are the consequences if there’s a translation error?”
- “Is this content going to external parties, regulators, or courts?”
The answers usually make the correct PE level obvious. If they don’t, share the project type matrix above and ask the client to identify which category their content falls into.
For recurring clients with mixed content types, consider creating a brief template that includes PE level as a required field, with the two definitions spelled out. This prevents the conversation from happening reactively when a project is already in flight.
A note on managing expectations: clients who come from a background of human translation sometimes expect MT-based workflows to be dramatically cheaper, with similar quality. The honest framing is: full PE saves you 20-40% compared to human translation costs, and speeds up delivery significantly - that’s real value. But it’s not “free translation with a quick read-through.” It’s a different workflow with different quality characteristics, at a meaningfully lower price point.
FAQ¶
What’s the difference between light and full post-editing?¶
Light PE (LAPE per ISO 18587) means fixing only the most serious errors so the text is understandable - style, flow, and minor issues are left in place. Full PE (FAPE) brings the output to publishable human-translation quality: accurate meaning, correct terminology, consistent style, proper grammar. The core question: does this text need to be understandable or publishable?
How much should I charge for light vs full post-editing per word?¶
Market rates in 2024-2025: light PE $0.02-0.05 per word, full PE $0.08-0.15 per word, versus human translation $0.15-0.30 per word. About 50% of translators don’t offer any discount for MTPE work, arguing that post-editing requires comparable effort to translating from scratch when MT quality is low. Always run a sample before committing to per-word rates.
How many words per hour can a translator post-edit?¶
Experienced post-editors average around 1,000 words/hour for light PE and 700 words/hour for full PE, versus 200-300 words/hour for human translation. These numbers vary significantly by language pair and MT quality - some combinations show almost no speed advantage. English-to-French MTPE can be 130% faster than human translation; other pairs may show no gain.
Can light post-editing be used for legal or medical documents?¶
No. Legal, medical, and any content with direct liability implications requires full PE at minimum. ISO 18587 explicitly positions light PE for content where “good enough” comprehension is the goal. For court filings, regulatory submissions, published technical manuals, or patient-facing materials, only full PE or human-only translation is appropriate.
How do I handle a light PE job that turns out to need full PE?¶
Stop, document what you’re seeing with specific examples, and contact the PM before continuing. Show evidence: “this paragraph alone requires complete structural revision - that’s full PE work.” Most clients accept rate adjustments when shown concrete evidence. Build a scope-change clause into every MTPE contract before starting.
Does ISO 18587 define post-editor qualifications?¶
Yes. ISO 18587:2017 specifies that full PE post-editors must have translation competence, linguistic expertise in both languages, research competence, and knowledge of MT systems. Light PE has slightly relaxed requirements but still demands language expertise. Any provider claiming certified MTPE services should be able to demonstrate ISO 18587 compliance.
What’s the main reason MTPE projects go over budget?¶
Misclassification - ordering light PE for content that genuinely needs full PE. A 2025 survey of 212 freelancers found 66% say MT output requires significant edits, meaning many light PE briefs are full PE jobs in disguise. The second cause: not running a diagnostic sample before committing to per-word rates on a large batch.
Sources¶
- ISO 18587:2017 - Translation services: Post-editing of machine translation output - international standard defining LAPE, FAPE, and post-editor qualifications
- Slator: How Fast Can You Post-Edit Machine Translation? - productivity benchmarks for light and full post-editing
- Swiss Global: Translation Productivity 2026 - Human Translation vs MTPE - comparative productivity data by language pair, including the EN-FR and EN-SV case studies