Contains verified C-corp COA procedures, account numbering decision trees, and Form 1120 tax-line mappings that produce more precise answers than reasoning from general training alone. Account type taxonomy (1xxx-9xxx), hierarchical grouping, book-tax differences, equity accounts (APIC, retained earnings, treasury stock), and COA restructuring. Consult when choosing account numbers, classifying accounts, mapping GL to tax lines, or asking "what account for X."
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Structural foundation for GL account design and classification in C-corporations under
Structural foundation for GL account design and classification in C-corporations under US GAAP. Covers the five root account types, standard numbering ranges, hierarchical grouping, C-corp equity accounts, and Form 1120 tax-line mapping.
Every GL account belongs to exactly one of five root types that determine which financial statement it appears on and its normal balance direction.
Balance Sheet accounts (cumulative, carry forward):
Income Statement accounts (periodic, reset at year-end close):
Contra accounts reverse the normal balance of their parent type (accumulated depreciation is contra-asset with credit balance; sales returns is contra-revenue with debit balance).
Standard 4-digit ranges for C-corporations. Leave gaps between active accounts for future inserts — at least 10 between accounts, 100 between categories.
Group parent/child accounts numerically (1500 PP&E group → 1510 Land, 1520 Buildings). Mirror contra accounts near their parent (1520 Buildings → 1720 Accum Depr – Buildings). Separate deductible from non-deductible expenses at the account level to simplify M-1 reconciliation.
Accounts form a tree: group (parent) accounts aggregate child balances for reporting; only leaf (detail) accounts receive postings. 3–4 levels is typical for mid-market C-corps (root type → classification → sub-group → detail).
Assets [group — no posting]
├── Current Assets [group]
│ ├── Cash and Equivalents [group]
│ │ ├── 1010 Operating Checking [leaf — postable]
│ │ ├── 1020 Payroll Checking [leaf]
│ │ └── 1030 Money Market [leaf]
│ └── Accounts Receivable [group]
│ ├── 1200 Trade Receivables [leaf]
│ └── 1210 Allowance for Doubtful Accounts [leaf, contra]
├── Fixed Assets [group]
│ ├── 1510 Land, 1520 Buildings, 1530 Equipment [leaves]
│ └── 1720 Accum Depr – Buildings, 1730 Accum Depr – Equipment [contra leaves]
└── ...
Year-end close: Revenue (4xxx) and expense (5xxx–9xxx) accounts net to Income Summary, which transfers to Retained Earnings (3200). Dividends Declared (3500) also closes to Retained Earnings.
Design the COA so each account maps to a specific Form 1120 line. Key mappings:
Income — 4000 gross revenue → Line 1a, 4100 returns → Line 1b, 4800 interest income → Line 5, 4810 dividends → Line 10 (Schedule C for DRD), 4900 rents → Line 6, 8100 asset sale gains → Line 8 (Schedule D / Form 4797)
Deductions — 6000 officer comp → Line 12, 6010 wages → Line 13, 6300 repairs → Line 14, 7200 bad debts → Line 15, 6100 rents → Line 16, 7100 taxes/licenses → Line 17, 8000 interest → Line 18, 7300 contributions → Line 19 (10% limit), 6800 depreciation → Line 20 (Form 4562), 6900–7999 other → Line 26
Non-deductible (M-1/M-3 add-backs) — 7400 penalties (IRC §162(f)), 7410 50% meals (IRC §274), 7420 entertainment (100% post-TCJA), 9000 federal income tax, 8200 unrealized gain/loss
Timing (deferred tax — reverse in future periods): depreciation (GAAP straight-line vs. tax MACRS/bonus per IRC §168), revenue recognition (ASC 606 vs. constructive receipt), bad debt (allowance vs. direct write-off per IRC §166), prepaids (matching vs. 12-month rule), deferred revenue (GAAP vs. Rev. Proc. 2004-34), Section 179 expensing.
Permanent (never reverse): meals 50% disallowed (IRC §274), entertainment 100% disallowed post-TCJA, fines/penalties (IRC §162(f)), federal income tax, tax-exempt interest, DRD 50/65/100% (IRC §243), officer life insurance premiums (IRC §264), political contributions (IRC §162(e)).
Separate accounts for items with different tax treatment at the GL level — deductible meals vs. entertainment in separate accounts, officer comp separate from staff wages, depreciation by asset class if book/tax methods differ, interest expense by purpose if §163(j) applies.
Read these for deeper detail on specific topics:
references/ccorp-coa-design.md — Expanded version of the content above with full sub-range tables, detailed tree examples, complete Form 1120 mapping tables, and extended book-tax difference analysis with IRC citations. Read when you need the detailed lookup tables or are building a COA from scratch.references/accounting-system-architecture.md — Accounting system architecture showing how COA concepts map to system implementation. Read section 2 for the account data model (root_type, report_type, account_type fields, nested set tree), section 3 for GL entry validation rules, section 9 for how the financial report engine uses account hierarchy, section 14 for period closing mechanics.references/guide-cpa-expert.md — Authoritative source bibliography. Read §2 for FASB ASC topic index and Big 4 technical guides, §3 for IRC section references and IRS publications (Pub 542, 535, 946, Form 1120 instructions).For platform-specific COA implementation:
qbo-integration:qbo-coa for QBO account creation, detail types, tax-line mapping within QBO, special QBO accounts and pitfallsqbo-integration:qbo-api for programmatic COA management via the QBO APIFor related foundation knowledge:
accounting-foundation:categorization-rules for transaction-to-account routing logicaccounting-foundation:financial-statements for presentation requirements that depend on account classificationaccounting-foundation:entity-profile for corporate entity details that affect COA design (entity type, fiscal year, ownership structure)bookkeeping:transaction-processing — account classification for categorizationtax-prep:form-1120-prep — tax-line mappings for return preparationtax-prep:tax-planning — book-tax difference analysisfinancial-planning:budgeting-forecasting — account hierarchy for budget structurenpx claudepluginhub aeyeops/aeo-basis-plugin-marketplace --plugin accounting-foundationGuides financial statement preparation, analysis, and plain-language explanation of accounting concepts for small business owners.
Designs or overhauls financial reporting systems including chart of accounts, accounting framework selection (GAAP/IFRS), close calendar, and management reporting packages.
Routes accounting questions to the narrowest specialist agent. Classifies and dispatches queries, never answers directly.