Automated Bank Reconciliation Using Regex and AI
Match transactions and reconcile accounts in minutes instead of hours
The Reconciliation Time Sink
Bank reconciliation is essential but time-consuming. Traditional reconciliation of 200 monthly transactions can take 4-6 hours. Bookkeepers must manually match each bank transaction to general ledger entries, identify discrepancies, and investigate variances.
With regex pattern matching and AI assistance, you can reduce this to 30-45 minutes while actually improving accuracy.
The Regex + AI Reconciliation Method
Phase 1: Data Preparation
Use regex to standardize both data sources:
// Bank statement cleaning 1. Extract amounts: \$[\d,]+\.\d{2} 2. Extract dates: \d{2}/\d{2}/\d{4} 3. Clean descriptions: Remove reference numbers, codes // General ledger cleaning 1. Standardize GL amount format 2. Normalize GL dates to same format 3. Extract check numbers: CHECK #(\d+)// Bank statement cleaning 1. Extract amounts: \$[\d,]+\.\d{2} 2. Extract dates: \d{2}/\d{2}/\d{4} 3. Clean descriptions: Remove reference numbers, codes // General ledger cleaning 1. Standardize GL amount format 2. Normalize GL dates to same format 3. Extract check numbers: CHECK #(\d+)Phase 2: Exact Matching with Regex
Create composite keys for automatic matching:
Match Key Pattern: Date + Amount + First word of description Regex: (\d{4}-\d{2}-\d{2})\s+\$([\d,]+\.\d{2})\s+([A-Z]+) Example: Bank: "2025-11-15 $500.00 AMAZON PURCHASE" GL: "2025-11-15 $500.00 AMAZON" Match Key: "2025-11-15|500.00|AMAZON" Result: ✓ Exact MatchMatch Key Pattern: Date + Amount + First word of description Regex: (\d{4}-\d{2}-\d{2})\s+\$([\d,]+\.\d{2})\s+([A-Z]+) Example: Bank: "2025-11-15 $500.00 AMAZON PURCHASE" GL: "2025-11-15 $500.00 AMAZON" Match Key: "2025-11-15|500.00|AMAZON" Result: ✓ Exact MatchPhase 3: Fuzzy Matching with AI
For non-exact matches, use AI:
AI Fuzzy Matching Prompt:
"Match these bank transactions to GL entries: Bank: 2025-11-15 | $505.00 | AMAZON.COM*AB12 GL Options: A) 2025-11-15 | $500.00 | Amazon Office Supplies B) 2025-11-15 | $505.00 | Office Supplies C) 2025-11-16 | $505.00 | Amazon Which is the best match? Consider: - Amount matches exactly (B, C) - Date matches exactly (A, B) - Vendor name similarity Most likely match: B (same date, exact amount)"
Identifying Unmatched Items
Bank Items Not in GL
After regex matching, remaining items are unmatched. AI Prompt: "These bank transactions have no GL entry: 1. 2025-11-10 | $45.00 | BANK FEE 2. 2025-11-15 | $1,200.00 | DEPOSIT XYZ CORP For each: - Suggest likely GL category - Identify if it's a missing entry or legitimate unrecorded item - Recommend correcting action"After regex matching, remaining items are unmatched. AI Prompt: "These bank transactions have no GL entry: 1. 2025-11-10 | $45.00 | BANK FEE 2. 2025-11-15 | $1,200.00 | DEPOSIT XYZ CORP For each: - Suggest likely GL category - Identify if it's a missing entry or legitimate unrecorded item - Recommend correcting action"GL Items Not in Bank
GL entries without bank matches might be: - Checks not yet cleared (pattern: CHECK #\d+) - Pending deposits - Accruals (pattern: ACCRUAL|PREPAID) - Errors AI analyzes context to determine whichGL entries without bank matches might be: - Checks not yet cleared (pattern: CHECK #\d+) - Pending deposits - Accruals (pattern: ACCRUAL|PREPAID) - Errors AI analyzes context to determine whichAutomated Reconciliation Workflow
- Extract bank data Use regex to pull date, amount, descriptionExtract bank data
Use regex to pull date, amount, description
- Extract GL data Same fields from accounting systemExtract GL data
Same fields from accounting system
- Standardize formats Regex patterns ensure apples-to-apples comparisonStandardize formats
Regex patterns ensure apples-to-apples comparison
- Exact match (regex) ~70-80% match automaticallyExact match (regex)
~70-80% match automatically
- Fuzzy match (AI) ~15-20% matched with AI intelligenceFuzzy match (AI)
~15-20% matched with AI intelligence
- Flag exceptions (AI analysis) Remaining 5-10% flagged with explanationsFlag exceptions (AI analysis)
Remaining 5-10% flagged with explanations
- Manual review Bookkeeper reviews only flagged itemsManual review
Bookkeeper reviews only flagged items
Advanced Pattern Matching
Check Number Matching
Bank Pattern: CHECK #(\d+).*\$([\d,]+\.\d{2}) GL Pattern: Check (\d+).*\$([\d,]+\.\d{2}) Match if: - Check numbers identical (Group 1) - Amounts identical (Group 2) - Dates within 5 days (AI validates)Bank Pattern: CHECK #(\d+).*\$([\d,]+\.\d{2}) GL Pattern: Check (\d+).*\$([\d,]+\.\d{2}) Match if: - Check numbers identical (Group 1) - Amounts identical (Group 2) - Dates within 5 days (AI validates)ACH/Wire Transfer Matching
Pattern: (ACH|WIRE|EFT)\s+([A-Z0-9]+) Extract transaction ID (Group 2) Match by ID + amount AI handles variations in descriptionPattern: (ACH|WIRE|EFT)\s+([A-Z0-9]+) Extract transaction ID (Group 2) Match by ID + amount AI handles variations in descriptionDiscrepancy Analysis
| Issue | Regex Detection | AI Resolution |
|---|---|---|
| Timing difference | Same amount, off by 1-3 days | Analyze if reasonable delay |
| Amount off by cents | Pattern: within $0.10 | Suggest rounding issue |
| Missing transaction | No regex match found | Categorize as unrecorded |
| Duplicate entry | Exact pattern match 2x | Verify if legitimate |
Time Savings Analysis
| Task | Manual | Regex+AI | Savings |
|---|---|---|---|
| Match 200 transactions | 4-6 hours | 15-30 min | 90% faster |
| Find discrepancies | 1-2 hours | 5 min | 95% faster |
| Document variances | 30 min | 2 min | 93% faster |
Professional Reconciliation Services
We use advanced automation to deliver same-day reconciliation services with exceptional accuracy.
Call (951) 203-9021Conclusion
Bank reconciliation automation represents one of the highest-value applications of regex + AI in bookkeeping. By using regex for precise pattern matching and AI for contextual intelligence, bookkeepers can reduce reconciliation time by 90% while improving accuracy and catching issues that might be missed in manual review.
