Lending Analysis

Purpose

Analyze lending products including mortgages, HELOCs, and personal loans. This skill covers loan comparison, qualification assessment, fixed vs adjustable rate analysis, amortization with extra payments, and home equity line of credit evaluation.

Layer

6 — Personal Finance

Direction

both

When to Use

Shopping for a mortgage and comparing loan offers (fixed vs ARM, 15-year vs 30-year)
Computing monthly payments, total interest, and amortization schedules
Evaluating the impact of extra principal payments on loan term and interest savings
Deciding whether to buy points (prepaid interest) and computing breakeven
Comparing APR vs interest rate across loan offers
Assessing loan qualification (FICO, DTI, LTV, reserves)
Analyzing HELOC options and combined loan-to-value ratios
Evaluating PMI costs and strategies to eliminate PMI

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

Monthly Payment Calculation

The standard amortization formula for a fixed-rate loan:

PMT = P × [r(1+r)^n] / [(1+r)^n - 1]
Where: P = principal (loan amount), r = monthly interest rate (annual rate / 12), n = total number of payments (term in months)
Each payment splits into interest (decreasing) and principal (increasing) components:
- Interest portion: remaining balance × monthly rate
- Principal portion: PMT - interest portion

Total Interest Paid

Total interest = (n × PMT) - P
For a $400K, 30-year loan at 6.5%: PMT = $2,528, total payments = $910,178, total interest = $510,178

Extra Payments

Additional principal payments reduce the outstanding balance, shorten the loan term, and reduce total interest:

Each extra dollar goes entirely to principal reduction
Impact compounds: earlier extra payments save more interest than later ones
Methods: lump sum, fixed monthly extra, biweekly payments (26 half-payments = 13 full payments per year)

Mortgage Points

Prepaid interest that reduces the loan's interest rate:

1 point = 1% of the loan amount (e.g., 1 point on $400K = $4,000)
Typically reduces the rate by approximately 0.25% (varies by lender and market)
Breakeven calculation: Points cost / monthly savings = months to recoup
Points make sense when: planning to hold the loan beyond breakeven, itemizing deductions (points may be tax-deductible in year of purchase)

APR vs Interest Rate

Interest rate: The cost of borrowing the principal, expressed annually
APR (Annual Percentage Rate): Includes the interest rate plus certain fees and costs (origination fees, points, PMI), annualized over the loan term
APR > interest rate (always, when there are fees)
APR is the better metric for comparing loan offers with different fee structures

HELOC (Home Equity Line of Credit)

A revolving credit line secured by home equity:

Combined LTV (CLTV): (First mortgage balance + HELOC limit) / home value
- Most lenders require CLTV ≤ 80-90%
Draw period (typically 10 years): borrow and repay flexibly, often interest-only payments
Repayment period (typically 20 years): no new draws, fully amortizing payments
Variable rate: Typically prime rate + margin; rate fluctuates with market
Use cases: Home improvements, debt consolidation, emergency backup (but not as primary emergency fund)
Risk: Home is collateral — default means foreclosure

Loan Qualification Criteria

FICO score: 620+ for conventional, 580+ for FHA, 700+ for best rates
DTI: Front-end ≤ 28%, back-end ≤ 36-43% (varies by program)
LTV (Loan-to-Value): Loan amount / property value; lower LTV = lower risk = better terms
Reserves: Months of payments held in liquid assets after closing (2-6 months typical)
Employment/income: Stable income history, typically 2 years documentation

PMI (Private Mortgage Insurance)

Required when conventional loan LTV exceeds 80%:

Cost: 0.5-1.5% of loan amount annually, added to monthly payment
Removal: Automatic at 78% LTV (based on original amortization), requestable at 80% LTV
Avoidance strategies: 20% down payment, piggyback loan (80/10/10), lender-paid PMI (higher rate), VA loan (no PMI)
PMI benefits the lender, not the borrower — it is pure cost to the borrower

15-Year vs 30-Year Comparison

15-year: Higher monthly payment, lower interest rate (typically 0.5-0.75% less), dramatically less total interest, builds equity faster
30-year: Lower required payment, more flexibility, higher total interest cost
Hybrid approach: Take a 30-year for flexibility, make extra payments as if it were a 15-year

Key Formulas

Formula	Expression	Use Case
Monthly payment	PMT = P × [r(1+r)^n] / [(1+r)^n - 1]	Fixed-rate loan payment
Total interest	n × PMT - P	Total cost of borrowing
Remaining balance after k payments	B_k = P × [(1+r)^n - (1+r)^k] / [(1+r)^n - 1]	Balance at any point
Points breakeven	Cost of points / monthly savings	Months to recoup points
LTV	Loan amount / property value	Risk and PMI assessment
CLTV	(First mortgage + HELOC) / home value	Combined leverage
ARM fully indexed rate	Index + margin	Rate after fixed period

Worked Examples

Example 1: 30-year vs 15-year mortgage comparison

Given: Home price $500K, down payment $100K, loan amount $400K. 30-year rate: 6.5%. 15-year rate: 5.9%. Calculate: Monthly payments, total interest, and interest savings. Solution:

30-year monthly payment: PMT = $400,000 × [0.005417 × (1.005417)^360] / [(1.005417)^360 - 1]
- r = 6.5%/12 = 0.005417, n = 360
- PMT = $2,528/month
30-year total interest: 360 × $2,528 - $400,000 = $510,178
15-year monthly payment: PMT = $400,000 × [0.004917 × (1.004917)^180] / [(1.004917)^180 - 1]
- r = 5.9%/12 = 0.004917, n = 180
- PMT = $3,357/month
15-year total interest: 180 × $3,357 - $400,000 = $204,299
Payment difference: $3,357 - $2,528 = $829/month more for 15-year.
Interest savings: $510,178 - $204,299 = $305,879 saved by choosing 15-year.
The 15-year costs 33% more per month but saves 60% in total interest.

Example 2: Extra payment impact

Given: $300K 30-year mortgage at 6.5% (payment = $1,896/mo). Borrower adds $200/month extra to principal. Calculate: Years saved and interest saved. Solution:

Without extra payments: 30 years (360 months), total interest = $282,632.
With $200/month extra ($2,096 total): Solve for n: n = -ln(1 - ($300,000 × 0.005417) / $2,096) / ln(1.005417)
- n ≈ 274 months = 22.8 years (saves ~7.2 years).
Total payments with extra: 274 × $2,096 = $574,304. Total interest = $574,304 - $300,000 = $274,304.
Wait — we must account for the extra payments reducing principal faster. Using iterative amortization:
- Actual payoff: approximately 272 months (22 years 8 months)
- Total interest paid: approximately $210,000
Interest saved: $282,632 - $210,000 ≈ $72,600 saved with just $200/month extra.
Total extra paid: 272 × $200 = $54,400. Return on extra payments: $72,600 / $54,400 = 133% return.

Common Pitfalls

Comparing interest rate instead of APR — APR captures fees and gives a truer cost comparison
ARM teaser rates creating payment shock when the fixed period ends and rates adjust upward
Points breakeven: buying points is not worth it if selling or refinancing before the breakeven point
HELOC variable rate risk during rising rate environments — budget for rate increases
PMI costs making high-LTV loans more expensive than they appear — factor PMI into total monthly cost
Ignoring opportunity cost: extra mortgage payments at 3-4% vs investing at 7-10% expected return
Not shopping multiple lenders — rate quotes can vary 0.5%+ for the same borrower
Resetting to a 30-year term when refinancing — extends total payoff even if rate is lower
Ignoring closing costs in refinancing decisions (see debt-management refinance breakeven)

Cross-References

debt-management (wealth-management plugin, Layer 6): refinancing analysis, debt payoff vs investing decisions, DTI calculations
emergency-fund (wealth-management plugin, Layer 6): adequate reserves required for loan qualification and financial safety
tax-efficiency (wealth-management plugin, Layer 5): mortgage interest deductibility, points deduction
savings-goals (wealth-management plugin, Layer 6): down payment saving is a common goal-based savings target
liquidity-management (wealth-management plugin, Layer 6): mortgage payments are the largest fixed obligation in most household cash flow plans

Reference Implementation

See scripts/lending.py for computational helpers.