For simultaneous interpreting, the cognitive load is extremely high — interpreters must listen, comprehend, reformulate, and speak almost at the same time, all while monitoring accuracy, tone, and audience reaction. Because of this, the international standard (AIIC, ISO, UN, EU, etc.) sets clear guidelines:
| Setting | Typical Duration per Interpreter | Notes |
| Conference booth (simultaneous) | ~30 minutes per stint before switching | Interpreters work in pairs (or trios) and rotate every 20–30 minutes to prevent cognitive fatigue. (AIIC Asia-Pacific; NCIH) |
| Full workday (with rotation) | ~6 hours total interpreting time (including breaks and alternation) | The total workday may be 7–8 hours, but active interpreting time is split between partners. |
| Solo simultaneous interpreting | Max 1.5 to 2 hours (absolute limit) | Even the best professionals risk serious decline in quality and mental overload beyond this. (NIWAP). |
🕐 Practical Working Limits per Day
A reasonable, sustainable limit for professional simultaneous interpreters is:
- 2–3 sessions of 20–30 minutes each, alternated with a colleague
- Total “active interpreting” time: about 2.5–3 hours per day
- Total “on-site working time” (including standby and breaks): 6–8 hours
Even with breaks, after around 6 hours of total duty time, fatigue and accuracy degradation become noticeable.
🧩 Factors That Affect Endurance
| Factor | Impact |
| Experience & Training | More seasoned interpreters manage load better but still need rotation. |
| Working languages | Greater distance between source and target (e.g., Japanese → English) increases fatigue. |
| Subject matter | Technical or emotionally intense topics accelerate mental strain. |
| Sound quality & booth conditions | Poor audio, lack of ventilation, or inadequate lighting worsen fatigue. |
| AI-assisted or hybrid modes | May reduce monotony but often introduce new stress (e.g., monitoring accuracy, adapting to imperfect AI output). |
⚖️ Summary
As a rule of thumb, a professional simultaneous interpreter should not interpret more than 2–3 hours per day (spread over a full day with breaks) before fatigue significantly affects performance.
Standards & Professional Guidelines
1. AIIC (International Association of Conference Interpreters)
- Interpreters usually work in teams of at least two, taking turns—rotations every ~20-30 minutes—in simultaneous interpreting booths, to maintain concentration and quality. (AIIC Asia-Pacific)
- They define a “normal working day” of no more than two sessions per day of about 2½ to 3 hours each.
(FTC) - In shorter meetings (“shorter” depends on region/contract), fewer interpreters may be needed, but the rotation and relief still apply. (FTC)
2. Council / Contract Frameworks (e.g. for Remote or Virtual Interpreting)
For remote simultaneous interpreting work, there are frameworks that put limits such as:
- A single session maximum of 3 hours 30 minutes (Assortis)
- Two sessions max of 2 hours 30 minutes each, with at least 1 hour 30 minutes break between them. (Assortis)
3. ISO Standards
- ISO 20109:2025 — this standard is about the equipment for simultaneous interpreting (sound quality, etc.), not directly prescribing how long interpreters should work without fatigue. (ISO)
- There’s also a standard under development (ISO/FDIS 17651-3) about interpreters’ working environment, which will include recommendations related to hubs, rest, etc. (ISO)
4. Other Community / Regional Norms
- Many interpreter associations and service providers confirm the rotation every ~20–30 minutes to mitigate fatigue. (AIIC Asia-Pacific, Dragoman Language Solutions)
- Community interpreting guidelines (e.g. ISO 13611-2014) often include break timings: for example, when interpreting consecutively, or in simultaneous mode, allow break after maximum periods (15-30 min in some cases) to prevent performance drop. (Scribd)
※※※
1. “Best Practice: Team Interpreting.” National Immigrant Women’s Advocacy Project, https://niwaplibrary.wcl.american.edu/wp-content/uploads/LANG-Qref-TeamInterp.pdf
2. “Call for Tenders.” Assortis, https://www.assortis.com/public/upload/CoE774867.pdf
3. “FAQ about interpreting.” AIIC Asia Pacific, https://aiic.asia/faq/.
4. “Federal Trade Commission Decisions.” Federal Trade Comission (FTC), https://www.ftc.gov/system/files/documents/commission_decision_volumes/volume-123/vol123pg488-605.pdf
5. “ISO/FDIS 17651-3: Simultaneous interpreting — Interpreters’ working environment.” ISO, https://www.iso.org/standard/85017.html.
6. What’s in a Word? National Council on Interpreting in Health Care, https://www.ncihc.org/assets/documents/publications/Whats_in_a_Word_Guide.pdf.