Mid-Year Convention in DCF Interviews: Why Timing Changes Value

"Do you use a mid-year convention in your DCF?" separates people who memorized WACC from people who thought about cash timing. You do not need a perfect stub model in an interview. You need the intuition: annual cash flows do not all arrive on December 31. Say that first, then show the exponent.

The short answer

"A mid-year convention assumes free cash flow arrives evenly through the year, so I discount each year's cash flow as if it arrived at the midpoint. Year 1 is discounted by 0.5 periods, Year 2 by 1.5 periods, and so on. That usually raises present value versus year-end discounting because cash is assumed earlier. I use it for going-concern annual models; for near-term deals I prefer quarterly or explicit stubs."

Year-end vs mid-year

PV of Year t FCF = FCF_t / (1 + WACC)^t

PV of Year t FCF = FCF_t / (1 + WACC)^(t − 0.5)

So Year 1 uses exponent 0.5, Year 2 uses 1.5, and Year 3 uses 2.5. The WACC is unchanged; only the timing assumption moves.

Tiny numeric feel

Assume WACC = 10%, Year 1 FCF = 100.

Same cash, higher PV under mid-year. Across a full projection plus terminal value, the gap compounds because every period's cash is pulled forward by half a year relative to year-end convention.

Terminal value under mid-year

Be consistent. If explicit FCF uses mid-year, TV is often assumed at the midpoint of the terminal year or handled with a matching convention. Messy inconsistency is worse than a simple year-end model you can defend. If you exit via exit multiple on Year N EBITDA, say when you assume that exit cash arrives, then discount with a matching exponent.

When interviews expect mid-year

• Academic / textbook DCF walkthroughs
• Annual models for stable businesses
• When the interviewer is fishing for timing awareness
• When they ask why two DCFs with the same FCF and WACC disagree

When to prefer something else

• Monthly or quarterly project finance / RE models where explicit timing already exists
• Stub year to a transaction date
• Highly seasonal cash flows where the midpoint is a bad abstraction
• Distressed or turnaround cases with front-loaded or back-loaded cash

How it ties to WACC and TV

Mid-year does not change WACC itself. It changes when you assume cash is received relative to the valuation date. It also interacts with TV: a large TV means timing assumptions at the horizon still move EV. Candidates who obsess over mid-year while using a sloppy perpetuity growth rate are optimizing the wrong decimal.

Stub periods and deal dates

If you value a company in March with a December fiscal year, a stub may matter more than mid-year versus year-end philosophy. Say you would model cash from valuation date to year-end explicitly, then apply annual mid-year or year-end conventions to full years after that. Interviewers like hearing that you can escalate from convention to stub when the calendar demands it. Pair this with Stub Period Modeling when they press.

Common traps

1. Claiming mid-year changes WACC
2. Using mid-year on FCF but an inconsistent TV discount without saying so
3. Applying mid-year to a model that is already monthly
4. Forgetting that negative FCF years also move earlier, which can lower PV
5. Treating mid-year as mandatory rather than a timing approximation

30-second verbal

"Year-end discounting treats annual FCF as if it arrives at year end. Mid-year assumes average arrival at the midpoint, so I use exponents 0.5, 1.5, 2.5. That increases PV versus year-end when cash is positive. I keep terminal value consistent with that convention, or I switch to quarterly stubs when timing is material."

Practice

On a simple 3-year FCF stream, compute PV both ways at 10% WACC and narrate the percentage difference. Then return to the full DCF interview walkthrough and terminal value pages so the pieces connect. On Project Horizon, toggle timing assumptions and watch EV move without changing the FCF forecast itself.