Comparable Sales Adjustment Calculator
Builds a side-by-side comparable-sales adjustment grid the way an appraiser would: it takes the homeowner's subject home and a set of recent comparable sales, then adjusts each comp's sale price up or down for the measurable ways it differs from the subject - living area (square footage), bedroom/bath count, lot size, condition or features, and how long ago it sold. The result is an adjusted value for each comp and an indicated value range for the subject, so the homeowner can state a defensible opinion of value rather than a guess. The tool follows the standard sales-comparison logic used in mass appraisal - a comp that is superior to the subject is adjusted downward, a comp that is inferior is adjusted upward - and it uses a local dollar-per-square-foot rate the homeowner supplies (or the assessment district's own implied rate) plus an optional time adjustment to the valuation/lien date. It is a generic explainer of how adjustments work, not the production valuation engine, and it never tells the homeowner what their home is 'really' worth - it shows the math so they can defend it.
Example
Input: Subject: 2,000 sq ft. Comp A: sold $400,000, 2,200 sq ft (200 sq ft larger than the subject). Local living-area rate: $50 per sq ft. No time adjustment.
Output: Comp A is 200 sq ft LARGER than the subject, which makes it superior, so its sale price is adjusted DOWNWARD: 200 sq ft x $50/sq ft = $10,000. Adjusted value of Comp A = $400,000 - $10,000 = $390,000. With a single comp, the indicated value of the subject is $390,000; with more comps you would take the central tendency of all adjusted values.
Input: Subject: 2,000 sq ft, 3 bed / 2 bath. Rate: $50/sq ft living area; +$5,000 per extra full bath; time adjustment 6% per year to a Jan 1, 2026 lien date. Comp 1: $400,000, 2,200 sq ft, 3/2, sold Jul 1, 2025. Comp 2: $360,000, 1,850 sq ft, 3/2, sold Jan 1, 2025. Comp 3: $415,000, 2,050 sq ft, 3/3, sold Oct 1, 2025.
Output: Comp 1 ($400,000): size -$10,000 (200 sq ft larger x $50, superior -> down); time +$12,000 (6 months at 6%/yr ~= 3% x $400,000); adjusted ~= $402,000. Comp 2 ($360,000): size +$7,500 (150 sq ft smaller x $50, inferior -> up); time +$21,600 (12 months at 6% x $360,000); adjusted ~= $389,100. Comp 3 ($415,000): size -$2,500 (50 sq ft larger x $50, down); bath -$5,000 (one extra full bath, superior -> down); time +$6,225 (3 months at 6%/yr ~= 1.5% x $415,000); adjusted ~= $413,725. Adjusted comps range $389,100 - $413,725; the median ~= $402,000, which is the indicated value for the subject as of the Jan 1, 2026 lien date.
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