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How to Calculate Investment Metrics

This guide explains how to compute and view financial KPIs for your investment properties.

Automatic Calculation

The Real Estate Investor application automatically calculates investment metrics when you have the required data:

  1. Property — Purchase price and basic details
  2. Rental Income — Monthly rent and vacancy rate
  3. Operating Expenses — Property expenses (taxes, insurance, maintenance, etc.)

Using the Finance Utility Functions

Programmatic Calculation

You can trigger KPI calculations using the compute_analysis_for_property function:

from investor_app.finance.utils import compute_analysis_for_property
from core.models import Property

# Get a property
property = Property.objects.get(id=1)

# Calculate all metrics
analysis = compute_analysis_for_property(property)

# View results
print(f"NOI: ${analysis.noi}")
print(f"Cap Rate: {analysis.cap_rate * 100:.2f}%")
print(f"Cash-on-Cash: {analysis.cash_on_cash * 100:.2f}%")
print(f"IRR: {analysis.irr * 100:.2f}%")
print(f"DSCR: {analysis.dscr}")

Via Django Shell

python manage.py shell

from django.contrib.auth import get_user_model
from core.models import Property, RentalIncome, OperatingExpense
from investor_app.finance.utils import compute_analysis_for_property
from decimal import Decimal

User = get_user_model()
user = User.objects.first()

# Create a property
property = Property.objects.create(
    user=user,
    address="789 Investment Ave",
    city="Austin",
    state="TX",
    zip_code="78701",
    purchase_price=Decimal("400000")
)

# Add rental income
RentalIncome.objects.create(
    property=property,
    monthly_rent=Decimal("3000"),
    effective_date="2024-01-01",
    vacancy_rate=Decimal("0.05")
)

# Add operating expenses
OperatingExpense.objects.create(
    property=property,
    category="Property Tax",
    amount=Decimal("4800"),
    frequency="annual",
    effective_date="2024-01-01"
)

OperatingExpense.objects.create(
    property=property,
    category="Insurance",
    amount=Decimal("1800"),
    frequency="annual",
    effective_date="2024-01-01"
)

OperatingExpense.objects.create(
    property=property,
    category="Maintenance",
    amount=Decimal("300"),
    frequency="monthly",
    effective_date="2024-01-01"
)

# Calculate metrics
analysis = compute_analysis_for_property(property)

# Display results
print(f"\nProperty: {property}")
print(f"Purchase Price: ${property.purchase_price}")
print(f"\nFinancial Metrics:")
print(f"  NOI: ${analysis.noi}")
print(f"  Cap Rate: {float(analysis.cap_rate) * 100:.2f}%")
print(f"  Cash-on-Cash: {float(analysis.cash_on_cash) * 100:.2f}%")
print(f"  IRR: {float(analysis.irr) * 100:.2f}%")
print(f"  DSCR: {analysis.dscr}")

Viewing Metrics in Django Admin

  1. Navigate to http://localhost:8000/admin
  2. Click on Investment analyses under the CORE section
  3. View the calculated metrics for each property

Understanding the Calculations

Net Operating Income (NOI)

NOI = Annual Income - Annual Operating Expenses
  • Annual Income = Monthly Rent × 12 × (1 - Vacancy Rate)
  • Annual Expenses = Sum of all operating expenses (normalized to annual)

Cap Rate

Cap Rate = NOI ÷ Purchase Price

Expressed as a percentage (e.g., 0.059 = 5.9%)

Cash-on-Cash Return

Cash-on-Cash = Annual Cash Flow ÷ Total Cash Invested

In the MVP: - Annual Cash Flow = NOI (no debt service) - Total Cash Invested = Purchase Price

Internal Rate of Return (IRR)

IRR is calculated using a 12-month cash flow projection:

  • Month 0: -Purchase Price
  • Months 1-12: NOI ÷ 12

Debt Service Coverage Ratio (DSCR)

DSCR = NOI ÷ Annual Debt Service

In the MVP, DSCR returns 0 when there's no debt service (all-cash purchase).

Manual Calculation Examples

Example Property

  • Purchase Price: $350,000
  • Monthly Rent: $2,500
  • Vacancy Rate: 5%
  • Annual Property Tax: $4,200
  • Annual Insurance: $1,200
  • Monthly Maintenance: $200

Calculate NOI

Effective Monthly Income = $2,500 × (1 - 0.05) = $2,375
Annual Income = $2,375 × 12 = $28,500

Monthly Expenses = ($4,200 ÷ 12) + ($1,200 ÷ 12) + $200 = $650
Annual Expenses = $650 × 12 = $7,800

NOI = $28,500 - $7,800 = $20,700

Calculate Cap Rate

Cap Rate = $20,700 ÷ $350,000 = 0.0591 or 5.91%

Calculate Cash-on-Cash

Cash-on-Cash = $20,700 ÷ $350,000 = 0.0591 or 5.91%

(Same as Cap Rate in all-cash purchase scenario)

Recalculating Metrics

Metrics are stored in the InvestmentAnalysis model. To recalculate:

from investor_app.finance.utils import compute_analysis_for_property
from core.models import Property

# Recalculate for a specific property
property = Property.objects.get(id=1)
analysis = compute_analysis_for_property(property)

# Recalculate for all properties
for property in Property.objects.all():
    compute_analysis_for_property(property)
    print(f"Updated analysis for {property}")

Best Practices

  1. Add complete data — Ensure all rental income and expenses are entered
  2. Update regularly — Recalculate when income or expenses change
  3. Check assumptions — Verify vacancy rates and other assumptions
  4. Compare properties — Use consistent assumptions when comparing investments
  5. Account for all expenses — Don't forget property tax, insurance, HOA, utilities, etc.

Common Issues

Zero NOI

If NOI is zero, check: - Have you added rental income records? - Have you added operating expense records? - Are the effective dates correct?

Unexpected Cap Rate

If cap rate seems incorrect: - Verify purchase price is accurate - Check that expenses are properly categorized (monthly vs. annual) - Ensure vacancy rate is set correctly

IRR Calculation Errors

If IRR returns 0: - This may indicate the calculation failed (negative cash flows only) - Current MVP uses simplified 12-month projection - Future versions will support custom holding periods

Next Steps