sales-data-analysis/.cursor/rules/ltm_methodology.md

LTM (Last Twelve Months) Methodology Rules

⭐ RECOMMENDED: Use analysis_utils.py

Prefer utility functions:

from analysis_utils import get_ltm_period_config, get_annual_data, calculate_annual_metrics
from config import get_ltm_period, get_ltm_label

ltm_start, ltm_end = get_ltm_period_config()
year_data, year_label = get_annual_data(df, 2025, ltm_start, ltm_end)

What is LTM?

LTM (Last Twelve Months) = Rolling 12-month period for the most recent partial year

• Purpose: Apples-to-apples comparison with full calendar years
• Example: If latest data is through September 2025, use Oct 2024 - Sep 2025 (12 months)

When to Use LTM

• Full calendar years (2021-2024): Use complete year data
• Most recent partial year (2025): Use LTM if you only have partial year data
• Complete years only: Disable LTM in config if all years are complete

Configuration

Configure in config.py:

LTM_ENABLED = True  # Set to False if all years are complete
LTM_START_MONTH = 10  # Month number (1-12)
LTM_START_YEAR = 2024
LTM_END_MONTH = 9
LTM_END_YEAR = 2025

Implementation Pattern

from analysis_utils import get_ltm_period_config, get_annual_data

ltm_start, ltm_end = get_ltm_period_config()

for year in sorted(df['Year'].unique()):
    year_data, year_label = get_annual_data(df, year, ltm_start, ltm_end)
    # year_label will be "2025 (LTM 9/2025)" for LTM year, or "2025" for regular year

Labeling Requirements

ALWAYS label LTM year with notation in:

• Chart titles
• Chart x-axis labels
• Table headers
• Print statements
• Report text

Example:

from config import get_ltm_label

ltm_label = get_ltm_label()  # Returns "2025 (LTM 9/2025)" or None
if ltm_label:
    title = f'Annual Revenue Trend\n({ltm_label})'

Common Mistakes

❌ WRONG:

year_2025_data = df[df['Year'] == 2025]  # Uses partial year (not comparable)

✅ CORRECT:

from analysis_utils import get_annual_data
ltm_start, ltm_end = get_ltm_period_config()
year_2025_data, year_label = get_annual_data(df, 2025, ltm_start, ltm_end)

Disabling LTM

If all years in your analysis are complete calendar years:

# In config.py:
LTM_ENABLED = False

Then all years will be treated as full calendar years.