What is the USNCO?
The U.S. National Chemistry Olympiad (USNCO)is the American Chemical Society's annual high-school chemistry competition. Its purpose is to identify the four students who represent the United States at the International Chemistry Olympiad (IChO) each summer.
USNCO has been administered by the American Chemical Society since 1984. It runs through ACS Local Sections — geographic chapters of the society spread across the United States — each of which administers its own Local Exam and nominates top students to the National Exam. There is no single centralized testing facility; students take the Local Exam at their school or local proctored site under the supervision of the ACS Local Section that covers their region.
USNCO is distinct from regional, state-level, and university-invitational chemistry competitions in two ways: it is the official U.S. selection mechanism for the international team, and although USNCO publishes no formal syllabus, its exam content stays consistent across years and covers 10 well-defined topic areas that go well beyond a typical AP Chemistry course — including college general chemistry, organic chemistry, analytical chemistry, and hands-on laboratory work.
Who is eligible?
Eligibility tightens at each stage of the competition.
Local Exam. Open to any high-school student (typically grades 9-12; some Local Sections allow advanced 7th or 8th graders) enrolled at a U.S. high school within the section's geographic boundaries. No prior USNCO participation is required, and no citizenship requirement applies at this stage.
National Exam. Restricted to students nominated by their Local Section and — because this is the exam the international team is selected from — open only to U.S. citizens and permanent residents. Each section nominates a fixed allotment (typically 12; larger sections may have more) drawn from its top eligible scorers, under one further constraint: no more than two students per high school may advance, regardless of how many top scorers a single school has. This intentionally broadens school representation in the National Exam pool, but it also means competition intensity can vary substantially between Local Sections and between high schools. The detailed nomination mechanics — including how the per-school cap affects selection — are walked through on the USNCO Insider page.
Study Camp and IChO team. Reserved for the top 20 students nationally on the National Exam — the pool the four-member U.S. team for that summer's IChO is chosen from.
Local Sections differ in how they organize, schedule and proctor the Local Exam — ask the coordinator at the ACS Local Section that covers your school rather than assuming the standard arrangement.
The three stages
The USNCO progression takes a single school year. Each stage filters down to the next.
Stage 1 — Local Exam
~1,000+ advanceHeld in March each year. Administered by individual ACS Local Sections. Format is typically 60 multiple-choice questions in 1 hour 50 minutes, covering general high-school chemistry. Each section advances its own top scorers to the National Exam, subject to the per-school cap and the citizenship requirement described above — so nationally the field narrows to ~1,000+ students rather than to a single ranked list.
“Typically” is doing real work in that sentence: not every Local Section uses the ACS Local Exam. Some set their own paper — the Northeastern Section is the best-known example — and others nominate by different means entirely. Check with the section that covers your school rather than assuming the standard format, and see the USNCO Insider page for how nomination actually works.
Stage 2 — National Exam
Top 190 awardedHeld during a ~10-day window in early-to-mid April. Three parts: Part I (multiple choice, 1 hour 30 minutes), Part II (8 free-response problems covering reaction writing, quantitative chemistry, and organic chemistry, 1 hour 45 minutes), and Part III (a hands-on laboratory practical, 1 hour 30 minutes). Awards reach roughly the top 190 nationally: the top 50 of those earn High Honors and the rest earn Honors, with additional students below that line receiving Honorable Mention.
Stage 3 — Study Camp
Top 20 nationallyTwo-week intensive program held at the University of Maryland in early June. The top 20 students from the National Exam are invited. Includes advanced instruction, laboratory training, and multiple rounds of theoretical and practical selection exams. The four students with the highest combined performance form the U.S. IChO Team for that summer's International Chemistry Olympiad; the 5th and 6th ranked students are designated first and second alternates.
Exam format
The National Exam is the centerpiece of the competition and has three structurally distinct parts.
Part I — Multiple Choice
60 questions in 1 hour 30 minutes. The paper is not a grab bag: ACS builds it from 10 topic blocks of 6 questions each, in a fixed order — Stoichiometry/Solutions, Descriptive/Laboratory, IMFs/States of Matter, Thermodynamics, Kinetics, Equilibrium, Redox/Electrochemistry, Atomic Structure/Periodicity, Bonding/Molecular Structure, and Organic/Biochemistry — so every block is worth exactly 10% of the paper and none can be safely skipped. The Local Exam is built from the same 10 blocks. Tests speed, breadth, and rapid pattern recognition; each question carries equal weight in the raw Part I score.
See all 10 blocks and which session covers each one →
Part II — Free Response
1 hour 45 minutes of 8 extended-response problems. The first question is always a set of reaction-equation prompts where students must complete and balance chemical reactions across organic, inorganic, and biochemical contexts. Subsequent problems cover quantitative chemistry: detailed thermodynamic analysis, kinetics derivations, multi-step mechanism work, and inorganic structural reasoning. Part II discriminates strongly among serious contenders. The dcho.us Reaction Writing Study Guide covers all 163 reaction-writing questions from 1999-2025.
Part III — Laboratory Practical
1 hour 30 minutes of hands-on laboratory work. Typical procedures include titration, qualitative analysis, kinetics measurements, and quantitative determination of an unknown. Scored on procedural technique, data analysis, and final answer accuracy. Part III only counts toward Study Camp selection — not Honors or High Honors ranking. The dcho.us USNCO Lab Practical Guide documents Part III procedures and analysis from 2015-2025.
Scoring and award tiers
Tier-specific score formulas determine the Honors and High Honors cohorts as well as Study Camp selection. The lab practical (Part III) is weighted only for Study Camp selection.
| Tier | Cohort | Score formula |
|---|---|---|
| Study Camp | Top 20 nationally | Part I × 1.25 + Part II + Part III × 0.5 |
| High Honors | Top 50 nationally | Part I × 1.25 + Part II |
| Honors | Within the top 190, below High Honors | Part I × 1.25 + Part II |
| Honorable Mention | Additional students below the Honors line | — |
Part III carries the lightest weight of the three, but it decides more Study Camp places than that weight suggests: the students in contention are clustered within a few points of one another, so the half-weighted lab score is often what separates an invitation from a near miss. Exact cutoff scores fluctuate slightly each year with exam difficulty. For full selection mechanics, including how Local Section nomination caps affect who reaches the National Exam, see the USNCO Insider page.
2026-2027 calendar
Provisional milestones for the current cycle.
These dates carry over the 2025-2026 calendar and are published for planning only — USNCO headquarters confirms the 2026-2027 dates in September. ACS sets the National Exam window (typically a ~10-day window in early-to-mid April), and each Local Section schedules the exam within that window — specific dates can vary by section. Local Exam dates also vary slightly by section. For the dcho.us program calendar — including instruction modules and bootcamps that align with these milestones — see /programs.
How to prepare
Preparation strategy depends on the target tier and the student's starting point.
Local Exam qualification
A student with a solid year of high-school chemistry (or AP Chemistry in progress) and 6-12 months of focused review typically has a strong shot at Local Exam advancement. Emphasis: breadth, stoichiometric fluency, and rapid multiple-choice technique.
National Exam awards (Honors or higher)
12-18 months of preparation covering organic chemistry, physical chemistry, and olympiad-style problem solving in depth. Part II reaction-writing proficiency becomes the discriminator. Mock exams with detailed analysis separate Honors from High Honors.
Study Camp / IChO team
A multi-year commitment, typically begun in 9th or 10th grade and sometimes earlier. The usual shape of it: reach the National Exam and win an award there in 10th or 11th grade, then push on to Study Camp and the IChO team in 11th or 12th. Coverage runs well beyond AP level — advanced organic structures and reactivities, descriptive chemistry and reactions, inorganic structure, and analytical lab technique — with sustained year-round practice including frequent mock exams. By that point knowledge and skills have to be both broad and deep, with no module left weak, and speed and accuracy on problem solving at a very high level.
For students unsure of where to start, the dcho.us Find Your Level wizard gives a personalized recommendation in about two minutes. Available in English and 中文.
Free study resources
These resources are published openly on dcho.us — free, no enrollment, usable by any USNCO student regardless of coaching program.
- USNCO Exam Topics — The 10 blocks the multiple-choice papers are built from, each mapped to the session that teaches it across Levels 2, 3 and 4.
- USNCO Reaction Writing Study Guide — Every Part II reaction-writing question from 1999 through 2025, with worked answers and a first-principles framework. Filterable by year, reaction type, and topic.
- USNCO Lab Practical Guide — Part III procedures, analysis, and scoring breakdowns from 2015 through 2025.
- USNCO Mock Exam System — Free. Sit full papers under exam timing or work through them untimed, and get scored the moment you submit — with topic-by-topic analytics and a worked explanation for every question.
- USNCO Learning Objectives — Every objective behind those ten blocks, split Standard and High Level, on the mock platform (free account).
- Recommended USNCO Textbooks — Curated list of reference and problem books organized by competition level and topic.
- Decoding of Chemistry Olympiad (YouTube) — Dr. Chen's free video series covering USNCO problems, reaction-writing strategy, lab practical preparation, challenging topics, learning objectives, and study strategies.
- USNCO Award Check — Look up historical USNCO results by school and by ACS Local Section, alongside community-reported National Exam cutoffs for each section — the closest thing there is to knowing where the bar sits near you.
- USNCO Insider — Selection mechanics: nomination funnel, per-school cap, score formulas, and award tiers.
Dr. Chen's Academy programs
Beyond the free reference materials, Dr. Chen's Academy offers structured coaching programs aligned with the three USNCO progression tiers.
Level 2
Local Prep
For students with one year of solid chemistry experience targeting Local Exam qualification.
Level 3
National Prep
For students with AP Chemistry mastery (or equivalent) preparing for the National Exam.
Level 4
Camp Prep
For advanced students targeting High Honors and Study Camp selection.
Full pricing, schedule, and module-level detail are on the programs page; the curriculum page compares the levels side by side and maps every session to the 10 exam blocks. Outcomes — 10+ IChO medalists, 40+ Study Camp qualifications, 200+ National Exam awards across 15+ years — are detailed on /achievements.
Frequently asked questions
What is the USNCO?
The U.S. National Chemistry Olympiad (USNCO) is the American Chemical Society's annual high-school chemistry competition. It selects the four-member U.S. team that represents the United States at the International Chemistry Olympiad (IChO) each summer. USNCO has been administered by ACS since 1984 and runs through the network of ACS Local Sections across the country.
Who is eligible to take the USNCO?
Any high-school student (grades 9-12 typically; some Local Sections allow younger students) enrolled at a U.S. high school may take the Local Exam, the first stage — there is no citizenship requirement to sit it. Advancement to the National Exam is reserved for the top performers in each Local Section, is capped at two students per school regardless of how many high-scorers a school has, and is open only to U.S. citizens and permanent residents, because the National Exam is where the international team is selected from. Local Sections vary in how they organize and proctor the Local Exam — check with the ACS Local Section that covers your school.
What are the stages of the USNCO competition?
The USNCO competition runs in three stages each year. Stage 1 — the Local Exam — is held in March; each ACS Local Section nominates its own top scorers, and ~1,000+ students nationwide reach the next stage. Stage 2 — the National Exam — is held during an ACS-set ~10-day window in early-to-mid April and consists of three parts: Part I (60 multiple-choice questions, 1 hour 30 minutes), Part II (8 free-response problems including reaction equations, quantitative chemistry, and organic chemistry, 1 hour 45 minutes), and Part III (a hands-on laboratory practical, 1 hour 30 minutes). Roughly the top 190 on the National Exam receive awards, with the top 50 of those earning High Honors and the rest earning Honors. Stage 3 — the Study Camp — is held in early June at the University of Maryland and brings together the top 20 nationally for two weeks of intensive instruction and competition. The four students with the highest combined performance at Study Camp form the U.S. IChO team.
How is the USNCO scored?
The National Exam uses tier-specific score formulas. Awards reach roughly the top 190 students nationally, ranked on a Part I × 1.25 + Part II composite: the top 50 of those earn High Honors and the rest earn Honors. The Study Camp cohort (top 20) is selected on Part I × 1.25 + Part II + Part III × 0.5 — the lab practical only counts toward Study Camp selection. Honorable Mention recognizes additional students below the Honors line. The exact cutoff scores fluctuate slightly each year based on exam difficulty.
When are the USNCO exams held?
The 2026-2027 USNCO cycle follows the standard schedule: Local Exam late Feb - mid Mar, 2027, National Exam mid Apr, 2027, and Study Camp early Jun, 2027. Those dates carry over the 2025-2026 calendar and stay provisional until USNCO headquarters confirms them in September. ACS sets the National Exam window (typically a ~10-day window in early-to-mid April), and each Local Section schedules the exam within that window — specific dates can vary by section. Local Exam dates also vary slightly by section.
How do I qualify for the USNCO Study Camp?
The Study Camp is reserved for the top 20 students nationwide on the National Exam, ranked on the formula Part I × 1.25 + Part II + Part III × 0.5. Practically, a Study Camp invitation requires strong performance across all three parts — particularly the Part III lab practical, which only counts toward Study Camp selection. Students who reach the Study Camp typically have multi-year preparation: deep mastery of general, organic, physical, inorganic, and analytical chemistry; hands-on lab experience; and exposure to olympiad-style problem solving. See the detailed selection mechanics on the USNCO Insider page.
What study materials should I use to prepare for the USNCO?
Strong preparation combines textbook foundations, problem-solving practice on real past exams, and (for the Part II reaction-writing section) targeted reaction-mechanism work. Recommended textbook starting points by competition level and topic are listed on the Recommended Textbooks page on dcho.us. The Reaction Writing Study Guide on dcho.us covers all 163 reaction-writing questions from USNCO Part II across 1999-2025, with worked answers and a first-principles framework. The Lab Practical Guide covers Part III procedures and analysis from 2015-2025. The free Mock Exam System lets students sit full papers timed or untimed with immediate analytics, and the Award Check site shows historical results and community-reported cutoffs by Local Section. All of these are free to any USNCO student regardless of coaching program.
How long does USNCO preparation typically take?
Preparation timelines depend on starting level and target outcome. A student aiming for Local Exam qualification (entry to the National Exam) typically prepares 6-12 months with a solid AP Chemistry foundation. A student targeting National Exam awards (Honors or higher) typically prepares 12-18 months covering organic chemistry, physical chemistry, and olympiad-style problem solving in depth. A student targeting Study Camp typically commits multi-year preparation starting in 9th or 10th grade, with sustained year-round practice. Dr. Chen's Academy structures this as a three-level progression — Local Prep (Level 2), National Prep (Level 3), and Camp Prep (Level 4).