The formula,
not a black box.

What goes in

• The county's sale list. Parcel number, address, the amount due (the opening bid) and the sale date, from each county's own listing. The official source is checked daily, and a person reviews each update before it is published.
• The county assessor's record. Square feet, bedrooms, baths, year built, appraised and assessed value, property class, lot acreage where the county publishes it, and the building grade where it exists (Clayton).
• Comparable sales. Recent sold homes from third-party real-estate data, swept from the parcel's own ZIP code first and from its whole city when the ZIP turns up too few, in a 12-month window (24 in a small market). The pool is narrowed to homes within a quarter of the parcel's size and, where the county publishes bedroom counts, within one bedroom of it, then ranked by recency and similarity; up to ten are used for the valuation and the five ranked first count twice. A comp's postal city can differ from the parcel's. Each comp keeps its sale month, price, size and coordinates, so the worked examples can print how far away it is.
• Not an input. Liens, title, mortgages, occupancy and interior condition are not checked. Nobody visits the property.

Every parcel is routed to one of three models

• Residential. The assessor confirms a structure (a size, a bedroom count or a year built) and the class is not commercial or industrial. This is the only model that produces an ARV, a rehab estimate, an ROI, a max bid and a deal score.
• Vacant land. No structure. The land value is anchored to the county appraisal, never a recent land sale, so land is shown as an estimate and never scored or ranked. Raw land with no comps, a lot below the build floor, or vacant land in a floodplain is screened out as NO BID.
• Commercial, industrial and multi-family. Acquisition cost only: no ARV, no ROI, no score. Residential comps cannot value these parcels, so they are marked for a specialist valuation and the county figures are shown instead.

ARV, rehab and the cost stack

• ARV is a weighted mean price per square foot times the parcel's square feet. Of the comps used (up to ten, ranked by recency and similarity), the five ranked first count twice and the rest once; a comp with no recorded size is left out of the per-square-foot figure. If the result strays more than 30% from the county appraisal on thin support (fewer than five comps, a weak pool or a relaxed size match), or more than 50% regardless, the county appraisal is used instead and the record says so.
• Rehab is square feet times a rate times a 15% contingency. The county's building grade sets the rate where it exists (Excellent or Good $35, Average $55 a square foot); otherwise age does: built within 20 years $35, 20 to 45 years $55, older $85. Unknown size is priced as 1,400 square feet at the heavy rate.
• All-in cost is the opening bid plus rehab plus a flat $3,500 for legal and closing (the quiet-title allowance), $500 for an inspection and $4,200 of carrying cost ($350 a month for 12 months). Selling costs are 7% of the ARV.
• Post-rehab ROI is net profit (ARV less selling costs less all-in) divided by the all-in cost, computed at the opening bid. Returns above 200% are shown at that ceiling and marked, because figures that high usually mean a comp pool that does not fit the parcel.

What the score and "strong 75+" mean

The score maps the post-rehab ROI onto one curve: an ROI of 50% or more scores 80 to 100 (100 at 100% ROI), 30 to 49% scores 60 to 79, 20 to 29% scores 40 to 59, and under 20% scores 0 to 39. Breakeven and money-losing parcels score 0, and an ROI above 150% does not raise the score further.

The comp-confidence tier then caps it: High keeps the score, Medium caps it at 80, Low caps it at 50, and Estimate only sets it to 0 and withholds the bid. An improved parcel in a floodplain loses 15 points.

Strong (75+) is the bar the county pages count: a score of 75 or more, which on the curve means an ROI of at least 45% at the opening bid with at least Medium confidence. Inside the dashboard, Top deal is a higher bar: ROI of 100% or more at the opening bid, an ARV priced from comps rather than the appraisal fallback, at least 3 comps, not Low confidence, and an ROI no higher than the 200% ceiling.

How much to trust the number

• High. Five or more comps, a dispersion of 15% or less around their median (the IAAO coefficient of dispersion), a strong pool, and comps under 91 days old.
• Medium. Three or more comps with dispersion of 20% or less, or a High pool whose comps are 91 to 180 days old.
• Low. Two comps, or dispersion above 20%. The score is capped at 50 and the bid is pulled halfway toward the assessor-implied value when that is lower.
• Estimate only. One comp or none. No score and no bid; the county figures are shown.

What the comps do and do not tell you

• Comps come from the parcel's ZIP code, or from its whole city when the ZIP has too few recent sales, and are matched on size and, where the county publishes it, bedroom count (Cobb publishes none). They are not matched on street or neighborhood, and a comp's postal city can differ from the parcel's.
• Comps are not filtered by distance. A comp can be miles from the parcel, and the worked examples print the straight-line distance so you can judge it. Check each comp's location before you rely on the ARV.
• When the primary sales source is unavailable, a second source's recently inactive listings stand in for sold prices, and the record names the source. Comps can be a few months old by sale day.
• Liens are not checked. Neither is title, occupancy or interior condition. Order a title search and look at the property before you bid.
• The county keeps revising its list until sale day; parcels are frequently redeemed and removed. An unlock on a parcel pulled before the sale is credited back.

Where the recommended max bid comes from

On a house with enough comps to trust the anchor and a county appraisal, the max bid starts from an as-is anchor (the county's appraised value, or a distressed-sale figure when one exists), takes a fixed fraction of it, applies a risk factor, and subtracts a fixed allowance for quiet title, barment and 12 months of carrying cost. It is capped at a fixed share of the anchor and is never less than the opening bid.

The risk factor starts with a discount for the right of redemption that every Georgia tax deed carries, drops further with two or fewer comps and again when the as-is value is uncertain, and has a floor. The exact fractions are part of the paid analysis and are not published here; each worked example prints the resulting max bid beside the figures it was built from. On thin comps, land and commercial parcels the max bid is the opening bid: BidWise does not chase what it cannot value.

The Georgia rules every bid is priced against

Each priced parcel carries two labelled returns, never blended: the return if the owner redeems in the first year (the 20% premium on the bid, O.C.G.A. § 48-4-42) and the post-rehab return if the right of redemption is barred and the buyer keeps the property. The redemption calculator runs the premium math for any bid.

How the scores are distributed right now

• A comp pool from the wrong part of a city prices a parcel wrong; the appraisal guard catches the large misses, not the small ones.
• County records have gaps. Cobb publishes no bedroom or bath counts, and some parcels carry no coordinates.
• Rehab is a rate times size; it has not seen the inside of the house.
• Every figure is an estimate from public records, not an appraisal, and not investment, legal or tax advice.