Choosing whether to build dark fiber or buy access (IRU/lease) comes down to net economics under real market conditions: density (demand), permitting drag, construction risk, and the value of getting to revenue sooner. The framework below lays out the decision logic, shows the drivers in a quick table, and includes a calculator that turns your local assumptions into a clear “Build” or “Buy” recommendation.

Fiber Build vs Buy

A decision framework by market density and permit risk—plus a working NPV calculator.

What changes the answer

Market density (demand concentration, ARPU, route uniqueness)
Permit risk & make-ready (time, cost, uncertainty)
Capex per mile vs IRU price curve
Time-to-market value and outage/MTTR exposure

When “Build” tends to win

High density + scarce routes (defensible control)
IRU pricing steep or term too short
Long-lived demand and stable O&M

When “Buy” tends to win

Permitting drag makes delays costly
Short contract horizons or uncertain demand
Attractive IRU bundles with fast delivery

Core Drivers & How They Influence the Decision

Driver	Pushes Toward	Why It Matters
Market Density	Build when high	More demand over time amortizes capex; control adds strategic value.
Permit Risk & Delay	Buy when high	Schedule slips erode NPV and delay revenue.
Capex per Mile	Buy if high	Cost inflation, rock, bridges, rail crossings raise build hurdle.
IRU One-Time & MRC	Build if steep	Over long terms, IRU streams can exceed build + O&M.
O&M per Mile	Buy if high	Break/fix & locate costs accumulate; rural spans may be pricier to maintain.

Build vs Buy Calculator (NPV & Score)

Route & Market

Route miles Market density (0–100) Permit risk (0–100) IRU term (years)

Build Cost Assumptions

Capex per mile ($) Make-ready per mile ($) Attachments per mile ($) Handholes/splices per mile ($) O&M per mile per year ($) Build delay (months) Tip: leave 0 to auto-estimate from permit risk

Buy (IRU/Lease) Assumptions

IRU one-time per mile ($) IRU annual per mile ($) Cross-connect/NNI one-time ($) Buy delivery lag (months)

Financial & Timing

Discount rate (annual %) Cost escalation (annual %) Time-to-market value per month ($) Economic value of being live one month earlier Outage/MTTR penalty ($/yr) Optional: expected downtime cost

Recommendation will appear here

Press Calculate to see NPV, score, and drivers.

Build (NPV)

—

Includes capex + O&M + delay penalty

Buy (NPV)

—

Includes IRU one-time + annual + lag

Score & Perspective

Score: — (−100 = Buy, +100 = Build)

Sensitivity (single-factor)

— After you calculate, this will show how ±10% changes in key inputs move the decision.

Notes: NPV discounts annual streams; build delay defaults to an estimate from permit risk if left at 0. Score scales the NPV difference into a −100 to +100 band for an easy read.

Quick Glossary

IRU: Indefeasible Right of Use. Typically a large upfront plus recurring fees.

Make-ready: Work to prepare poles/ducts; often schedule-critical.

Time-to-market value: Economic value per month for launching sooner.

NPV: Present value of all cash flows using a discount rate.

Use this as a first pass, then tune the defaults to your market. If your IRU quotes improve or your permitting outlook worsens, you’ll see the recommendation swing. For executive readouts, export the NPV numbers and sensitivity notes to show exactly which levers move the decision in your geography.