Why It Matters
You're underwriting a 32-unit apartment building and your broker hands you a rent comp sheet. Before you trust it, you want a second source. CoStar is where that second source lives. It tracks verified lease transactions, current and historical vacancy by submarket, tenant move-in and move-out data, and sale comparables with actual cap rates — not estimates. The platform is the dominant data infrastructure for commercial brokers, lenders, and institutional investors. For smaller residential investors, it's often overkill, but once you're evaluating properties with five or more units, BLS data and ACS surveys tell you labor market and demographic story; CoStar tells you what deals are actually trading for. It's the difference between macro context and transactional reality.
At a Glance
- Coverage: Commercial real estate across the U.S. — multifamily (5+ units), office, retail, industrial, mixed-use, land
- Core data: Comparable sales with verified cap rates, lease comps, vacancy by submarket, tenant roster with move-in/move-out dates, building-level financials
- Pricing: Approximately $5,000–$10,000+ per year for a single-market subscription; enterprise rates for multi-market access
- Owned by: CoStar Group, which also owns Apartments.com, LoopNet, Homes.com, and BizBuySell
- Access alternatives: LoopNet (free version, limited data), local commercial brokers who share CoStar pulls, some public libraries
How It Works
What CoStar actually contains. The platform is built on a research team that calls, emails, and verifies every commercial real estate transaction and lease event it can find. When a 24-unit apartment building sells in a secondary market, CoStar's researchers attempt to confirm the sale price, cap rate, buyer, seller, and financing structure. The result is a database of verified comparables — not just public record scrapes — that includes lease comps showing actual tenant names, square footage, rent per square foot, lease start date, and lease term. For multifamily, this means you can see what a similar 1990s garden-style apartment complex in your target submarket rented for across its unit mix, not just an aggregated average. That specificity is what separates CoStar from free alternatives.
How investors use it in due diligence. Before making an offer on a commercial property, most experienced investors or their brokers pull a CoStar report for the subject property and a comp set. The report shows trailing vacancy by submarket (so you know whether your deal is sitting in a 4% vacancy corridor or a 12% one), recent sale comps sorted by asset class and vintage, and in-place lease information when tenants are known. For value-add multifamily, the most useful feature is the rent comp stack — you can pull every lease event in a submarket over the past 24 months and see exactly where effective rents have landed after concessions. That number is your real market rent, and it's often 5–10% below the asking rents that get quoted in broker pitch decks. Cross-referencing with FRED economic data helps you understand whether that gap is narrowing or widening.
The CoStar Group ecosystem. CoStar Group is not just a data platform — it's a portfolio of real estate marketplaces. Apartments.com is the dominant residential rental listing site. LoopNet is the largest commercial property listing marketplace in the U.S. BizBuySell handles business-for-sale listings. The subscription data product (CoStar) feeds into these marketplaces, which in turn generates more transaction data. This flywheel gives CoStar a structural advantage: every listing on LoopNet or Apartments.com enriches the underlying analytics database. For investors, it means that Realtor.com and Redfin are the residential counterparts — useful for residential comps — while CoStar owns the commercial intelligence layer that residential platforms simply don't replicate.
Real-World Example
Blake is evaluating a 16-unit apartment complex in a mid-sized Sun Belt city. The listing broker claims market rents in the submarket are averaging $1,340 per month and vacancy is running around 5%. The asking price implies a 6.1% going-in cap rate.
Blake's commercial broker pulls a CoStar submarket report. What it shows: effective rents (after concessions) are averaging $1,271 per month over the trailing 12 months — about 5.1% below the broker's figure. Submarket vacancy is 8.3%, not 5%, and has trended upward for three consecutive quarters. Three comparable sales in the past 18 months transacted at cap rates between 6.7% and 7.4%.
Blake reprices the deal using CoStar's figures. At $1,271 effective rent, 8% vacancy, and a market cap rate of 7.0%, the building is worth roughly $187,000 per unit — not the $214,000 per unit the seller is asking. He counters at $189,000 per unit. The seller comes down. The deal closes $402,000 below ask, and Blake's underwriting reflects actual market conditions rather than broker narrative.
Pros & Cons
- Verified comparable sales with actual cap rates — not public record estimates or broker-supplied figures subject to selection bias
- Lease comp data showing tenant names, effective rents after concessions, and lease terms — critical for accurate rent underwriting
- Submarket-level vacancy trending by quarter, giving investors directional context that single-period snapshots miss
- CoStar Group's ownership of Apartments.com and LoopNet creates a data network effect that continuously enriches the underlying database
- Widely accepted as the institutional standard — lenders, appraisers, and equity partners all speak CoStar, so using it aligns your underwriting language with your capital partners
- Cost is prohibitive for most small investors — a single-market subscription runs $5,000–$10,000+ annually, making it impractical without commercial deal volume to justify it
- Data quality varies by market — primary metros like Dallas, Phoenix, and Atlanta have dense coverage; tertiary markets and rural areas have thinner comp sets with longer data lag
- Multifamily coverage skews toward larger assets (50+ units) — smaller portfolios of 5–20 unit buildings often have sparse comp coverage in the CoStar database
- Free-tier Realtor.com and Redfin residential data covers 1–4 unit properties more comprehensively than CoStar does at the small residential scale
- Subscription terms typically require annual commitments — there's no monthly trial, which makes it hard to evaluate before committing budget
Watch Out
Broker CoStar pulls are filtered by the broker's interest. When a selling broker hands you a CoStar report, it has been curated. Comp selection in CoStar is not automatic — the user chooses which properties to include in the comparable set. A broker motivated to support a high asking price will pull the most favorable comps and exclude the weaker ones. Always ask for the raw submarket report, not just the hand-selected comp set. If you're working with a buyer's broker, have them pull the report independently so you see the full picture.
Vacancy figures represent physical vacancy, not economic vacancy. CoStar tracks whether a space is leased, but it doesn't always capture the gap between contracted rent and effective rent after concessions, free rent periods, or tenant improvement allowances. In soft markets, a property can show 95% occupancy while the landlord is offering one to two months of free rent to fill units. That free rent is a real economic cost that doesn't appear in the vacancy figure. Always cross-reference CoStar vacancy data with the effective rent data from recent lease comps in the same submarket — the ACS survey income data can tell you whether the market can actually support those rents long-term.
CoStar data has a reporting lag in thin markets. In primary metros, CoStar's research team updates transactions and lease events within weeks. In tertiary markets or for off-market deals, the lag can stretch to three to six months or longer. If you're underwriting in a smaller market, the most recent CoStar comps may be six to twelve months old — which is significant when cap rates are moving. Supplement CoStar data with conversations with local commercial brokers who have ground-level intelligence CoStar's researchers haven't yet captured. Use BLS data to check employment trends that often lead real estate comps by six months.
Ask an Investor
The Takeaway
CoStar is the institutional-grade data backbone for commercial real estate underwriting. If you're evaluating commercial assets — especially multifamily buildings of 10 or more units — CoStar gives you verified comps, submarket vacancy trends, and lease data that free tools simply can't replicate. The cost is real: $5,000–$10,000+ per year per market. But so is the risk of underwriting a deal off unverified broker comps. Access it through your commercial broker if you don't have a subscription, pull the raw submarket report rather than the curated comp set, and combine it with FRED, BLS, and ACS survey data for a complete market picture. The investors who skip it are pricing deals based on what sellers want the market to look like — not what it actually is.