If you typed “what is the 820 rule?” you probably met a wall of conflicting answers. That’s because the phrase points to three very different ideas: a medical device quality regulation, a productivity rule of thumb, and a trading signal. I’ll make it easy: here’s what each one is, when to use it, and how to apply it without getting burned.

• It can mean the FDA’s medical device Quality System Regulation (21 CFR Part 820).
• Many people actually mean the 80/20 rule (Pareto principle): most results come from a few inputs.
• Traders use the “8/20 rule” for a short-term moving-average crossover signal.

Stick around for quick checklists and practical next steps for each use-case. We’ll also flag the traps that catch smart people off guard.

What people really mean by the “820 rule”

The term shows up in three main contexts. Before you go further, figure out which one matches your search intent. That’s how you avoid wasting time.

• FDA 21 CFR Part 820 (United States): The Quality System Regulation (QSR) that medical device makers must follow. If you design, make, or import medical devices into the U.S., this is your stop.
• 80/20 Rule (Pareto principle): A decision-making and productivity heuristic used in business, operations, and personal time management. If you want leverage and focus, this is it.
• 8/20 Moving Average Rule (trading): A technical analysis signal using the 8-period and 20-period moving averages to time entries and exits. If you’re backtesting systems or swing trading, this is the one.

Short on patience? The line you were probably looking for: the 820 rule in medical devices refers to the U.S. FDA’s 21 CFR Part 820 Quality System Regulation. If you meant the Pareto idea, it’s “80/20,” not “820.” If you meant trading, it’s “8/20.”

FDA 21 CFR Part 820: The medical device quality rule

21 CFR Part 820 is the FDA’s Quality System Regulation (QSR) for medical devices. It sets the baseline for how manufacturers design, make, package, label, store, install, and service devices sold in the United States. It covers both hardware and software (including SaMD) and applies to domestic and foreign manufacturers, contract manufacturers, and certain specification developers.

Authoritative source: The FDA’s Code of Federal Regulations, 21 CFR Part 820. In February 2024, the FDA issued the final Quality Management System Regulation (QMSR) rule to align with ISO 13485:2016; the effective date is February 2, 2026, with a transition period. Until then, Part 820 remains enforceable as written. Plan for the shift now.

Core requirements you’ll actually use:

• Management responsibility: defined quality policy, roles, and review cadence.
• Design controls: planning, inputs/outputs, verification/validation, risk management, and design transfer; maintain a Design History File (DHF).
• Document and change control: approved procedures, version control, and change review.
• Purchasing controls: supplier evaluation, selection, and monitoring; approved supplier list.
• Production and process controls: process validation (where output can’t be fully verified), environmental controls, equipment maintenance, and personnel training.
• Identification and traceability: batch/lot tracking, especially for implants and high-risk devices.
• CAPA (Corrective and Preventive Action): systematic identification of nonconformities, root cause, action, and effectiveness checks.
• Complaint handling and MDR: timely complaint evaluation; report adverse events where required.
• Servicing, labeling, packaging: defined procedures to prevent mixups and damage; label accuracy is non‑negotiable.
• Records: Device Master Record (DMR), Device History Record (DHR), training records, calibration logs. If it didn’t get recorded, it didn’t happen.

How to comply if you’re new (a pragmatic 10-step start):

1. Scope your devices and risk class. Map which parts of 820 apply. If you’re SaMD, put extra weight on design controls and risk management.
2. Adopt ISO 13485:2016 as your backbone now. The QMSR alignment kicks in 2026; starting with ISO 13485 eases audits and the transition.
3. Write a lean Quality Manual. Keep it short; link to SOPs for details. Auditors prefer clarity over volume.
4. Stand up document control. Use a simple eQMS or a disciplined folder + approval workflow. Version every SOP and form.
5. Build design controls early. Create a DHF; define inputs/outputs; trace risks to requirements, verification, and validation.
6. Qualify suppliers. Approve them against risk. Document criteria, audits (where appropriate), and ongoing checks.
7. Validate processes that you can’t inspect fully (e.g., sterilization, software build pipelines). Lock them with change control.
8. Set up CAPA and complaints. Don’t wait for a crisis. Start small with a clear intake, triage, root-cause template, and effectiveness checks.
9. Train, then record it. Everyone signs off on the procedures they use. Keep training fresh when SOPs change.
10. Run internal audits and management reviews. Close gaps before an FDA inspection; document decisions and follow-ups.

Pitfalls that cause 483s (and how to dodge them):

• Design controls bolted on at the end: start during concept, not after prototypes ship.
• CAPA files without clear root cause: use structured techniques (5 Whys, fishbone) and verify effectiveness.
• Supplier management on autopilot: re‑evaluate critical suppliers annually, especially those affecting safety.
• Records out of sync with reality: audit trails matter; use controlled forms and lock edits.
• Over‑engineering your QMS: more procedures than people can follow creates silent noncompliance. Trim to fit.

Quick example: A small team launching a connected glucose monitor maps user needs to design inputs, traces cybersecurity risks in their risk file, verifies firmware against requirements, validates the mobile app with real‑world usability tests, and documents installation and servicing steps. They qualify their PCB assembler, validate OTA update processes, and track complaints with a simple ticketing system that feeds CAPA. When the FDA inspector arrives, their DHF tells the whole story without anyone scrambling.

Credible references to know you’re on the right track: the FDA’s 21 CFR 820 text, the 2024 QMSR final rule preamble, and ISO 13485:2016. For usability, look at IEC 62366; for risk management, ISO 14971. Those aren’t niche-they’re the backbone of safe devices.

The 80/20 rule (Pareto principle): a leverage lens for work and life

The 80/20 rule says a small share of inputs drives a big share of outputs. The numbers aren’t magic; the shape is. Vilfredo Pareto observed power-law distributions in 1896 (wealth in Italy). In the mid‑20th century, quality expert Joseph Juran popularised the idea as the “vital few and trivial many” in defect reduction. Today you’ll see it everywhere from sales pipelines to inbox triage.

Where it shows up in the real world:

• Sales: a few products or customers produce the bulk of revenue.
• Customer support: a handful of recurring issues cause most tickets.
• Software: a few modules account for most bugs or performance wins.
• Personal productivity: a small set of high‑leverage tasks drives most progress.

How to apply it without making a mess:

1. Define the outcome you care about (revenue, uptime, exam score, weight loss, whatever).
2. List the inputs (features, clients, tasks, habits) and score them for impact and effort. If you have data, use it. If not, estimate.
3. Sort by impact per unit of effort. Circle the top 20%. That’s your “vital few.”
4. Double down on those inputs. Schedule them first. Allocate resources proportionally.
5. Deliberately deprioritise or kill the bottom 50%. Create a “not doing” list to protect focus.
6. Measure again in a month. The vital few shift over time-especially after you harvest the low‑hanging fruit.

Helpful heuristics:

• Use a 2×2: impact high/low vs. effort high/low. Tackle “high impact, low effort” first.
• Time block the vital few in the morning. Guard that time like a meeting with your future self.
• Cap work-in-progress. A simple WIP limit forces trade‑offs and keeps the 80/20 spirit alive.
• Beware false precision. The ratio might be 70/30 or 90/10. The point is skew, not exact math.

Evidence worth knowing: Pareto’s early work was in economics; Juran’s quality studies showed a small number of causes drive most defects in manufacturing. Modern operations research and business data often fit heavy‑tailed distributions, which is why the rule keeps popping up. You don’t need a PhD. You just need the courage to ignore the trivial many.

Everyday example: You sell six product SKUs. A quick look shows two SKUs bring in 76% of margin and drive most support calls. You focus the roadmap and marketing on those two, retire the worst performer, and cut build complexity. Three months later, you’re making more with less chaos and the team isn’t firefighting every afternoon.

The 8/20 moving average rule: a trader’s shortcut

Traders use the “8/20” as a moving‑average crossover. When the 8‑period moving average (often the Exponential Moving Average, EMA) crosses above the 20‑period, that’s a potential buy signal; a cross below is a potential sell or risk‑off signal. The idea is simple: let price confirm a short‑term trend shift before you act.

Basic setup:

• Choose your market and timeframe: daily charts for swing trading stocks or ETFs; 4‑hour for crypto; weekly for longer trends.
• Add 8‑EMA (fast) and 20‑EMA (slow). Some use SMAs-test both.
• Entry: fast MA crosses above slow MA; ideally above a higher‑timeframe trend filter (e.g., price above 200‑day).
• Exit: fast MA crosses back below slow; or use a trailing stop like 2× ATR; or partial exits at resistance.
• Risk: keep position size small enough that a normal stop‑out (e.g., 1-2× ATR) risks only 0.5-1% of equity.

Why it can work: Moving averages smooth noise and help you stick with trends. Why it fails: chop. In sideways markets, crossovers whipsaw you-small losses stack up. That’s not a bug; it’s the trade‑off for catching the occasional big trend.

Ways to improve robustness:

• Trend filter: Trade only when price is above the 200‑day MA (long) or below (short).
• Combine with structure: Take crosses that also break recent swing highs/lows.
• ATR-based stops: Place stops where normal noise won’t knock you out instantly.
• Limit trades during earnings or low‑liquidity sessions; spreads and gaps matter.
• Backtest properly: include slippage and fees; avoid peeking into the future; validate on out‑of‑sample data.

Concrete example: You test the S&P 500 ETF (SPY) on daily candles from 2000-2024. A basic 8/20 EMA crossover underperforms buy‑and‑hold when markets trend up strongly, but it reduces drawdowns and avoids some major bear market pain. Add a 200‑day filter and a 2× ATR stop and your equity curve smooths out, though you miss some V‑shaped rebounds. That’s the trade-you’re paying in whipsaws to sleep better at night.

Sanity note: There’s no universal “best” pair. 9/21, 10/30, or 5/20 are common variants. The right combo depends on your market’s noise and your temperament. If you can’t tolerate strings of small losses, trend trading with crossovers will frustrate you.

Cheat sheets, examples, FAQs, and what to do next

Bookmark this section. It compresses the how‑to into quick checks and answers the follow‑ups people usually ask.

FDA 21 CFR Part 820 / QMSR cheat sheet:

• Must‑haves: Quality Manual, design controls with traceability, document control, supplier control, production/process validation, CAPA, complaints, MDR (if applicable), DMR/DHR.
• Action this week: Draft your document control SOP, open your DHF, identify top 5 risks, and pick an eQMS or a lightweight approval workflow.
• Action this quarter: Supplier qualification, internal audit plan, first management review, at least one closed CAPA cycle.
• Transition prep: Map your QMS to ISO 13485:2016 now; track the FDA’s QMSR effective date (Feb 2, 2026) and plan training.

80/20 execution cheat sheet:

• Define one metric that matters (MOM revenue, NPS, exam score).
• List all inputs, score impact/effort, sort, circle the top five. That’s your vital few.
• Schedule those first. Create a “not doing” list. Review monthly.
• Measure results and re‑rank. Expect the mix to drift as constraints change.

8/20 trading checklist:

• Backtest your market and timeframe with fees/slippage.
• Pick entries/exits (crosses) and a stop method (ATR or structure‑based).
• Add a trend filter to reduce chop. Define max open risk.
• Journal every trade; tag reasons so you can improve rules, not vibes.

Mini‑FAQ

• Is the “820 rule” the same as the “80/20 rule”? No. 21 CFR Part 820 is a U.S. medical device quality regulation. The 80/20 (Pareto) rule is a heuristic about skewed outcomes.
• Does 21 CFR 820 apply to software as a medical device (SaMD)? Yes. Design controls, risk management (ISO 14971), and verification/validation apply to SaMD. Cybersecurity and usability fit into design inputs and risk controls.
• What’s changing with QMSR in 2026? The FDA’s 2024 final rule aligns Part 820 with ISO 13485:2016. Expect terminology shifts and closer harmonization. Use ISO 13485 now to ease the changeover.
• Is ISO 13485 “enough” for FDA? It helps a lot, but you must still meet applicable U.S. requirements (e.g., complaint handling specifics, MDR). Harmonization reduces the gap-not to zero.
• Is the 80/20 split always literally 80/20? No. It could be 70/30 or 90/10. The insight is that results are unevenly distributed.
• Which moving averages for 8/20-EMA or SMA? Many traders prefer EMAs for responsiveness, but there’s no rule. Test both on your market.
• Can the 8/20 rule work intraday? Sometimes, but microstructure noise increases whipsaws. If you try, confirm with higher‑timeframe trend and manage slippage.

Next steps and troubleshooting

• If you’re a med‑device founder: Assign a QMS owner, pick ISO 13485 as your framework, build a minimal Design History File this month, and schedule an internal audit. If you hit resistance, cut procedural fluff-keep only what your team can consistently follow.
• If you’re a manager chasing leverage: Run a one‑hour 80/20 workshop. Pick one metric, score tasks, move three bets to the top of the roadmap, and create a public “not doing” list. If everything shows up as “high impact,” your scoring is vague-tighten the metric.
• If you’re a retail trader: Backtest your 8/20 idea on your exact market with fees. If your curve dies in chop, add a 200‑day filter and ATR stop, or switch to a different strategy. If you can’t stick to the rules, lower size until your emotions settle.

Final note on credibility: For regulatory questions, rely on primary sources-the FDA’s 21 CFR 820 text and the 2024 QMSR final rule preamble-and recognized standards like ISO 13485 and ISO 14971. For the Pareto principle, J.M. Juran’s quality work gives the historical backbone. For trading, treat moving-average crossovers as tools to test, not truths to trust. That’s how you keep your decisions grounded and your outcomes cleaner.

Evelyn Marchant

I am a society analyst with a focus on lifestyle trends and their influence on communities. Through my writing, I love sparking conversations that encourage people to re-examine everyday norms. I'm always eager to explore new intersections of culture and daily living. My work aims to bridge scholarly thought with practical, relatable advice.

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