Lending

Handles mortgage and loan analysis with the formulas you'd otherwise paste into a spreadsheet. Covers the usual suspects: fixed versus ARM, 15 versus 30 year, amortization schedules, extra payment scenarios, whether buying points makes sense. Also does qualification checks (DTI, LTV, FICO thresholds) and HELOC combined loan-to-value calculations. The math is straightforward but tedious to do by hand, so this is useful when comparing offers or modeling what happens if you throw an extra $200 a month at principal. Includes PMI removal thresholds and APR versus rate comparisons. Basically a mortgage calculator that shows its work and explains the tradeoffs.

skills.sh installs: 741
GitHub stars: 224
last updated: Aug 21, 2026

View on GitHub

Install

$ npx -y skills add joellewis/finance_skills --skill lending --agent claude-code

Installs into .claude/skills of the current project.

Files

Lending Analysis

Core Concepts

Fixed-Rate Mortgage

The interest rate and monthly payment remain constant for the life of the loan:

Advantages: Predictable payments, protection against rising rates, simpler budgeting
Disadvantages: Higher initial rate than ARM, no benefit if rates decline (must refinance)
Most common terms: 30-year and 15-year fixed

Adjustable-Rate Mortgage (ARM)

Rate is fixed for an initial period, then adjusts periodically based on an index plus a margin:

Notation: 5/1 ARM = fixed for 5 years, adjusts annually thereafter; 7/1, 10/1 similarly
Fully indexed rate: Index (e.g., SOFR, 1-year Treasury) + margin (e.g., 2.75%)
Rate caps protect against extreme adjustments:
- Initial adjustment cap (e.g., 2%): maximum first adjustment
- Periodic cap (e.g., 2%): maximum change per adjustment period
- Lifetime cap (e.g., 5%): maximum total increase over initial rate
When ARM may be appropriate: Planning to sell or refinance before the fixed period ends, expecting rates to decline, or comfortable with rate variability