Here is a sensitivity-analysis exercise: a company has $100 million of debt, and rates rise by 0.25 percentage points. How much extra interest should go into your model?
The question is timely. On September 16, the Federal Reserve raised its target range to 3.75%–4.00%, a quarter-point increase.
For our hypothetical borrower, the answer will be $150,000 a year. The missing detail is which debt actually reprices. That detail is where the modeling begins.
Hypothetical full-year illustration. Constant balances; the floating rate resets by 0.25 percentage points. No hedges, floors, fees, or refinancing. This is an assumption, not a forecast of loan pricing.
The 60-Second Version
Read the debt terms: benchmark, spread, reset date, hedges, and maturity.
Follow the effect: interest expense, cash payments, and financing needs.
Review valuation inputs separately: a policy-rate move does not mechanically set WACC.
Contract, Calendar, Consequence: document what changes, when, and where it flows.
1. Start with the contract
Our borrower has two loans. The $60 million floating-rate portion initially costs 6%. For this exercise, assume its total rate resets to 6.25%, with the credit spread unchanged. The other $40 million is fixed at 6% and does not mature during the year.
Annual interest starts at $6 million. After the reset, the floating portion costs $3.75 million and the fixed portion costs $2.4 million. Total: $6.15 million.
The extra $150,000 is $60 million multiplied by 0.0025. Applying the increase to all $100 million would overstate the effect by $100,000 in this example.
In a real model, inspect the loan benchmark, spread, floor, and any hedge. A fixed-rate loan still deserves attention when it approaches refinancing. For debt in another currency, use the relevant local benchmark and terms.
2. Put the change in the right period
The $150,000 is an annualised effect. If the higher rate applies for only three months, the simplified extra expense is $37,500: $150,000 multiplied by 3/12. Actual calculations depend on reset dates, day-count rules, and outstanding balances.
Update the debt schedule first. Then let the model carry the expense into pre-tax profit and cash payments. Allow for the applicable tax treatment and payment timing, and check whether lower cash creates another borrowing need.
Keep the operating story separate. Higher financing costs alone do not change revenue or EBITDA. Demand, pricing, and operating costs need their own evidence. A rate announcement is a reason to review those assumptions, not enough information to rewrite them.
3. Revisit the discount rate separately
The Fed target is not the discount rate in your DCF. The cost of equity also depends on an appropriate risk-free yield, equity risk premium, and business risk. The cost of debt includes credit risk; the capital mix and tax treatment matter too.
Review the market inputs to your weighted average cost of capital, or WACC. Bond yields may already reflect an expected policy move. They can also respond to new information about growth and inflation.
That means a 0.25-point policy hike does not automatically justify adding 0.25 points to WACC. Use current, consistent inputs for the currency of the cash flows and document the reasoning.
If you want to practise how these pieces connect, Elite Membership includes financial modeling and valuation learning alongside Excel and AI. Start with a model whose debt schedule and assumptions you can follow.
4. Show the sensitivity without calling it a forecast
Try a deliberately simple valuation. Suppose a hypothetical business generates $10 million of unlevered free cash flow next year, growing at 2% indefinitely. With an 8% WACC, the growing-perpetuity value is $10 million divided by (8% minus 2%), or about $166.7 million.
Hold the cash flows and growth assumption constant and test a 9% WACC. The value falls to about $142.9 million. That is roughly 14% lower. At 10%, the value is $125 million.
Hypothetical growing perpetuity: value = next-year unlevered free cash flow / (WACC − growth). These discount-rate scenarios are independent assumptions, not predicted effects of the Fed decision.
The purpose is to see how much the conclusion depends on the discount rate. A full valuation needs a defensible forecast and terminal assumptions.
Keep the methods consistent. Unlevered cash flow is before interest and is discounted at WACC. Subtracting interest from that cash flow while still using WACC mixes financing into the calculation twice. Bridge enterprise value to equity value separately.
MAKE THE ASSUMPTIONS VISIBLE
Connect the debt schedule to the valuation
Explore financial modeling, valuation, Excel, and AI learning in Elite Membership. Practise how one input flows through a complete analysis.
5. Use Contract, Calendar, Consequence
Before sending the revised model, I would write a short change log using these three checks:
Contract: which benchmark, spread, fixed rate, or hedge determines the exposure?
Calendar: when does the debt reset or refinance, and for how much of the forecast period?
Consequence: which interest, cash, funding, and valuation outputs change, and which still rely on separate assumptions?
Add a base case and a clearly labelled stress case. Record why each input changed and compare the results with the previous version. The useful output is an explanation of what the business is exposed to and how much that exposure matters.
Reply and tell me where you would look first after a rate move: the debt schedule, the operating forecast, or the discount-rate assumptions. What would you need to know before changing a number?
Best regards,
Dheeraj Vaidya, CFA, FRM
Ex-JPMorgan & CLSA
Co-founder, WallStreetMojo
P.S. If you would like more practice connecting the statements and testing valuation assumptions, explore Elite Membership. Choose a modeling exercise and work through the links yourself. The newsletter stays free either way.
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