Why It Matters
Use the best case scenario to understand the upside potential of a deal—but never use it alone. Pair it with a base case and a worst case scenario to get a complete picture of risk and reward. A deal that only pencils in the best case is a deal you probably should not buy.
At a Glance
How It Works
The best case scenario is one leg of a three-scenario analysis framework. You build it by plugging in the most favorable values across every key variable:
Revenue assumptions: Rent at the high end of comparable units in the market. Vacancy at or near zero—perhaps 2–3% to account for routine turnover. No rent concessions, no collection loss.
Expense assumptions: Property taxes and insurance at current rates with no increases. Maintenance at the low end of historical norms. Management fees included but no large capital expenditure surprises.
Rehab assumptions: Project finishes on schedule and exactly on budget. No hidden structural issues, no permit delays, no contractor overruns.
Financing assumptions: You secure the best available rate, lock it in, and face no loan extension fees or surprise costs at close.
Once these inputs are set, you run the standard deal metrics—cash-on-cash return, net operating income, cap rate, and projected equity at exit—using the most favorable values for each. The output is your deal's ceiling: the best you could reasonably hope for.
The best case scenario is most useful as a sanity check. If the deal barely works even in the best case, it is too thin to pursue. If the best case shows strong returns, that tells you the upside is real—but it still does not tell you the most likely outcome. That is the base case's job.
Responsible investors use the three scenarios together:
- Best case — what happens if everything goes right
- Base case — what happens under normal, expected conditions
- Worst case — what happens if key assumptions break down
The spread between your best and worst case tells you how sensitive the deal is to variance. A narrow spread means the deal is relatively predictable. A wide spread means it carries meaningful execution risk.
Real-World Example
Rohan is analyzing a four-unit rental property. He builds three scenarios to evaluate the deal.
In his best case scenario, all four units rent at $1,450 per month—the top of the comparable range—from day one. He assumes 97% occupancy (one short vacancy period per year), expenses at 38% of gross income, and a rehab that wraps up in six weeks at the budgeted $42,000. At a 7.25% interest rate on his DSCR loan, the deal produces a 9.8% cash-on-cash return in year one.
In his base case, he models $1,350 rent, 92% occupancy, expenses at 43%, and a rehab that runs $48,000 over eight weeks. Cash-on-cash drops to 6.4%.
In his worst case, one unit sits vacant for three months, a plumbing issue adds $6,000 to the rehab, and rents come in at $1,250. Cash-on-cash falls to 2.1%.
Rohan's best case is strong. But his worst case still produces positive cash flow, which gives him confidence to move forward. He knows the deal works across a realistic range—not just under perfect conditions.
Pros & Cons
- Reveals the true upside potential of a deal before you commit capital
- Motivates deeper diligence by showing what is actually achievable
- Helps set performance targets for asset management after closing
- Useful for communicating opportunity to partners or lenders
- Establishes a benchmark to measure actual performance against
- Easy to misuse as the only scenario, leading to overconfidence
- Optimistic inputs can be unconsciously inflated to justify a deal you want to buy
- Does not reflect the most likely outcome—that is the base case
- Novice investors sometimes confuse the best case with a forecast
- Can create unrealistic expectations with passive investors or partners
Watch Out
The biggest danger with best case analysis is using it as your primary underwriting model. This is called "happy path" underwriting—modeling only the outcome where everything works—and it is one of the most common ways investors lose money.
Watch for these red flags in your own analysis:
Vacancy set to zero. Real properties have turnover. Even well-run units in strong markets see 5–8% annual vacancy. A 0% vacancy assumption in your best case is reasonable; carrying it into your base case is a mistake.
Rehab budget with no contingency. The best case can assume the project hits budget exactly. But if your base case also has no contingency line, your model is not a base case—it is an optimistic scenario mislabeled.
Rent above current market. Projecting top-of-market rent is valid in the best case only if comparable units are actually achieving that rate today. Projecting above current market is speculation, not analysis.
Treating best case returns as the pitch. If you are raising money from partners and you present only the best case numbers, you are misleading them. Always present all three scenarios.
The Takeaway
The best case scenario is a legitimate and valuable underwriting tool—but only when used as one part of a complete three-scenario framework alongside cash flow analysis, expense analysis, revenue analysis, rehab analysis, and financing analysis. It tells you what the deal could do if everything goes right. Use it to understand upside, set performance targets, and stress-test your assumptions—not to justify a deal that only works under ideal conditions.