dscr-tools 📊

Python toolkit for loan amortization, DSCR tracking, covenant monitoring, and loan sizing.

Supports multiple interest calculation methods, interest-only periods, ARM loans, max loan sizing, and stress testing — replacing bespoke Excel models with auditable, version-controlled Python code.

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Why dscr-tools?

Every commercial real estate and private credit analyst builds the same loan model from scratch in Excel. dscr-tools standardizes the engine so you can focus on the deal, not the spreadsheet.

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Installation

pip install dscr-tools

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Quickstart

from dscrtools import LoanParams, NOISchedule
from dscrtools.models import amortization, dscr, sizing, stress

loan = LoanParams(
    loan_amount=8_000_000,
    interest_rate=0.065,
    amortization_years=30,
    loan_term_years=10,
    interest_method="partial_io",
    io_periods=24,
    payments_per_year=12,
    property_name="Midtown Office Building",
)

noi = NOISchedule(
    base_noi=750_000,
    growth_rate=0.03,
    vacancy_rate=0.05,
    capex_reserve=10_000,
)

amortization.summary(loan)
dscr.summary_table(dscr.analyze(loan, noi, min_dscr=1.25))
sizing.size_loan(loan, noi=750_000, property_value=12_000_000)
stress.rate_shock(loan, noi, rate_shocks=[0.01, 0.02, 0.03])
stress.noi_stress(loan, noi, noi_haircuts=[0.10, 0.20, 0.30])

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Interest Methods

• fixed_30_360 - Fixed rate, 30/360 day count (most CRE loans)
• fixed_actual_360 - Fixed rate, Actual/360 (agency multifamily)
• fixed_actual_365 - Fixed rate, Actual/365 (some bank loans)
• interest_only - Full interest-only, no principal payments
• partial_io - Interest-only period followed by full amortization
• arm - Adjustable rate with floor and cap

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Modules

• amortization - Full period-by-period schedule with I/O and ARM support
• dscr - Annual DSCR calculation, covenant tracking, breach detection
• sizing - Max loan sizing via DSCR, LTV, and Debt Yield tests
• stress - Rate shock and NOI stress sensitivity tables
• loan - Interest calculation primitives for all day-count conventions

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DSCR Covenant Logic

• DSCR above min_dscr - OK
• DSCR below min_dscr - BREACH
• DSCR below 1.0 - DEFAULT

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Loan Sizing

Solves for the maximum loan amount that satisfies all three constraints simultaneously, identifying the binding constraint:

sizing.size_loan(loan, noi=750_000, property_value=12_000_000,
                 min_dscr=1.25, max_ltv=0.75, min_debt_yield=0.08)

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Running Tests

PYTHONPATH=. pytest tests/ -v

32 tests across all modules.

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Who This Is For

• CRE analysts underwriting commercial mortgage loans
• Private credit teams modeling leveraged deals
• Real estate finance practitioners replacing Excel waterfalls
• Anyone who needs reproducible, auditable loan math in Python

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License

MIT 2026 Jaypatel1511