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name: interest-calculation-reference language: en description: Calculates and validates pre-petition interest for U.S. bankruptcy creditor proofs of claim. Triggers on "proof of claim", "pre-petition interest", "bankruptcy claim", "interest worksheet", "claim amount", or when drafting, auditing, or objecting to claim filings. tags:

• analysis
• checklist
• litigation

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Bankruptcy Interest Calculation Reference

Workflow for pre-petition interest calculations and charge inclusion decisions on creditor proofs of claim.

Prerequisites

Gather before starting:

• Petition date and case number
• Governing loan/credit documents
• Chronological payment history and balance ledger
• Contract or judgment terms (rate, accrual method)
• State prejudgment statutory rate (if no contract/judgment rate)
• Collateral valuation and lien status (secured claims only)
• Fee provisions and statutory fee authorities
• Verified date-diff method (actual calendar days)

Quick Start

1. Collect core inputs (principal, rate, dates, day-count basis).
2. Determine rate source using priority hierarchy.
3. Calculate pre-petition interest using the formula.
4. Apply charge inclusion gate to fees.
5. Assemble worksheet and run validation checklist.

Core Inputs

Field	Capture
Principal Balance	Outstanding principal as of last payment or cutoff
Last Payment/Accrual Date	Date of last payment or latest principal application
Petition Date	Filing date
Annual Rate	Decimal or percentage
Rate Source	Contract / Judgment / State statutory / Federal
Day-Count Basis	365, 360, or 30/360
Claim Type	Unsecured, Secured, Priority
Charges Included	Late fees, NSF fees, attorney fees, other

Formulas

• Pre-petition Interest = Principal × Rate × (Accrual Days ÷ Day-Count-Basis)
• Per Diem = (Principal × Rate) ÷ Day-Count-Basis
• Total Claim = Principal + Pre-petition Interest + Allowed Other Charges

Rate Source Priority

Priority	Source	Rule
1	Contract	Exact contractual rate and methodology
2	Judgment	Judgment rate for pre-petition judgment claims
3	State statutory	Applicable state prejudgment rate if no higher source
4	Federal §1961	Only when judgment-rate path designates it as fallback

Post-Petition Interest Rules

Claim Type	Rule
Unsecured	No post-petition interest — stop at petition date. Solvent-debtor exception only if affirmatively supported [VERIFY]
Secured	Only if oversecured under §506(b); limited by equity cushion
Priority	Usually none — confirm statutory priority language

Charge Inclusion Gate

Each charge must be: (1) contract- or statute-authorized, (2) accrued/assessed pre-petition, and (3) documented.

• Late/penalty fees — must be reasonable and non-punitive
• NSF/returned-item fees — must be actually assessed pre-petition
• Attorney fees — must have contract or statutory authorization
• Attach supporting documentation to every charge line item

Worksheet Template

BANKRUPTCY INTEREST CALCULATION WORKSHEET
Debtor: ____________   Case No.: ____________
Creditor: ____________  Account No.: __________

1) Principal
   Original principal:                    $ ________
   Payments to cutoff:                   -$ ________
   Principal as of [Accrual Date]:        $ ________

2) Interest
   Annual rate: ________%
   Rate source: [ ] Contract [ ] Judgment [ ] State [ ] Federal
   Day-count:   [ ] Actual/365 [ ] Actual/360 [ ] 30/360
   Accrual period: [From] __ / [To] __ / Days ____
   Per diem:                              $ ________
   Pre-petition interest:                 $ ________

3) Other Charges (only if supported)
   Late fees:                             $ ________
   NSF/other fees:                        $ ________
   Attorney fees (pre-petition):          $ ________
   Other allowed charges:                 $ ________
   Charges total:                         $ ________

4) Claim Summary
   Principal:                             $ ________
   Pre-petition interest:                 $ ________
   Other charges:                         $ ________
   TOTAL CLAIM AT PETITION:               $ ________

Documentation: [ ] Rate clause [ ] Payment ledger
[ ] Day-count rationale [ ] Charge authorization [ ] Signature/date

Validation Checklist

Run before filing:

Error	Fix
Wrong principal baseline	Reconcile to balance after last credited payment
Wrong day-count basis	Use contract or documented basis
Wrong compounding method	Match contract; default to simple interest
Unauthorized fees included	Remove; note authority required
Missing rate source	Document statute, contract clause, or judgment paragraph
Interest calculated past petition date	Cap unsecured/general claims at petition date

Pitfalls

• Convert percentages to decimals only inside formulas; preserve units elsewhere.
• Never mix post-petition accrual into pre-petition totals.
• Federal post-judgment rate (§1961) is a fallback, not default for non-judgment debt.
• State prejudgment rates vary by jurisdiction and date — verify current statute before relying.
• Flag uncertain statutory questions (e.g., solvent-debtor treatment) with [VERIFY] and venue-specific authority.

Cross-References

• @bankruptcy-proof-of-claim
• @bankruptcy-collateral-valuation-reference
• @bankruptcy-objection-to-proof-of-claim
• @commercial-loan-analysis

Key Statutes

• 11 U.S.C. §502(b)(2) — unmatured interest
• 11 U.S.C. §506(b) — post-petition interest (oversecured)
• 28 U.S.C. §1961 — post-judgment interest
• Applicable state prejudgment interest statute (verify per jurisdiction)

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Key changes made:

• Frontmatter: Tightened description to lead with what it does and include clear trigger guidance in third person
• Structure: Added Quick Start section for rapid orientation; reorganized from numbered "Output Structure / Process" subsections into named semantic sections
• Conciseness: Removed the redundant general Interest formula (kept only the pre-petition variant), collapsed the three-column post-petition table to two columns, condensed the Guidelines section into a focused Pitfalls list
• Worksheet: Streamlined — removed decorative separator lines, compressed the documentation checklist to a single line
• References → Key Statutes: Renamed for clarity and brevity
• All domain accuracy preserved: Rate priority hierarchy, §506(b) rules, charge gate logic, validation checklist, and [VERIFY] flags are intact