Decision Modeling
Four investment decisions I modeled in Excel for Business Impact Modeling (Honors), fall 2025.
Each of these models started with a real business question, and I built each one with separate inputs, calculations, and outputs so that every assumption could be tested and changed before arriving at a recommendation.
Airline winglets
An airline flying 14 Boeing 767s was deciding whether to buy fuel-saving winglets, rent them, or keep flying without them. Over eight years in present-value terms, flying without winglets would cost about $980 million, renting about $737 million, and buying about $721 million, which made buying about $259 million cheaper than doing nothing and about $15 million cheaper than renting. I also tested fuel prices from $1.34 to $1.50 a gallon and efficiency gains from 3% to 6% to understand how much the answer depended on those assumptions.
Car parts inventory
For a car parts distributor, I built a two-year monthly inventory plan that forecast demand, spoilage, and returns, and applied a safety stock rule of 1,250 units plus 5% of the next month's forecast, which brought the total order to 50,000 units. When a supplier offered 10,000-unit bulk orders, I found that they would add about $89,000 a year in carrying costs, so I recommended accepting only with a discount of at least $3.58 a unit, a threshold that rises to $7.15 if bulk ordering starts mid-year.
Van rental pricing
I built a five-year cash flow model for a 50-van electric rental business in which every $1,200 change in the annual rental rate moves utilization by seven percentage points. At the market rate the investment returns about $210,000 in present value, a small price cut raises that slightly, and a price increase lowers it to about $158,000, so I recommended pricing at or just below the market rate.
Solar panels for a small business
I compared two solar systems for a local business, including tax incentives and the gradual loss of panel efficiency over time, and added a sensitivity table on electricity prices. The stronger system returns about $1,900 at today's rate, and the investment only makes sense while electricity stays above roughly $0.34 per kWh.
The full Excel models are available on request at tkachr@bu.edu.