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Usage Guide

This guide walks through how to use the MortgageAmortization CLI tool to simulate, analyze, and compare different mortgage loan structures.

Amortization Schedule

Generate a fixed-rate amortization schedule:

python -m cli.cli amortize \
  --type fixed \
  --balance 400000 \
  --rate 6.0 \
  --term 360

Optional arguments:

  • --extra-payment 200
  • --extra-frequency monthly
  • --recast-date 2026-01-01 --lump-sum 10000
  • --refinance-date 2026-01-01 --new-rate 5.25 --new-term 240 --refi-fees 3500
  • --output amortization.csv

ARM and HELOC

Simulate an ARM loan with index-based rate adjustments:

python -m cli.cli amortize \
  --type arm \
  --index SOFR \
  --margin 2.75 \
  --balance 400000 \
  --rate 5.0 \
  --term 360

Simulate a HELOC draw + repayment phase:

python -m cli.cli amortize \
  --type heloc \
  --balance 200000 \
  --rate 7.5 \
  --term 360 \
  --draw-period 120 \
  --repayment-term 240

Compare Scenarios

Visualize amortization curves across multiple loan options:

python -m cli.cli plot \
  --scenarios 400000 6.0 360 \
  --scenarios 400000 5.5 360 \
  --scenarios 400000 5.0 240

Effective APR

Compare true APR including points and fees:

python -m cli.cli compare-apr \
  --principal 400000 \
  --rate 5.75 \
  --term 360 \
  --points 1.0 \
  --fees 4500

Breakeven Calculator

Find breakeven point of a refinance:

python -m cli.cli breakeven \
  --monthly-savings 225 \
  --closing-costs 3500

Returns the number of months until refi pays off.

Other Tips

  • Output data to CSV via --output filename.csv
  • Dates must be in YYYY-MM-DD format
  • ARM simulations pull index rates from local data (see utils/data/macroeconforward.txt)

For more, explore: