Rate Base: the Asset That Earns
NARUC definition of utility rate base, why issuers use different labels, and FY2025 dollar bases and growth CAGRs for six large US utilities.
Educational analysis for professional use. This guide is not investment advice or a recommendation to buy or sell any security, and it is not personalised.
Rate Base Is the Regulated Asset That Earns
A US electric utility does not earn a market return on its entire balance sheet. It earns an authorised return on rate base: net investment in plant and assets used and useful in providing service. NARUC defines rate base as investor-funded plant in service on which regulators allow a fair return.
That base sits at the centre of every cost-of-service proceeding. The revenue requirement is return on rate base plus operating and maintenance (O&M) plus depreciation. Change the base, the allowed return, or the equity layer, and you change the dollars customers pay and the earnings shareholders receive.
The Label Zoo
Issuers rarely print a single line called “rate base” on the consolidated income statement. They use jurisdiction-specific labels that map to the same regulatory idea:
| Issuer label | Company | FY2025 base | Notes |
|---|---|---|---|
| Regulatory capital employed | NextEra FPL | $73.5B | 13-month average, FY2025 |
| Regulated earnings base | Duke Energy | $103.1B | End FY2025 |
| Rate base | Dominion Energy | $48.2B | End FY2025 |
| Rate base | Sempra | $57.0B | Up from $50B in 2024 |
| Segment rate-base proxies (derived) | American Electric Power | ~$77.6B | Sum of segments; no single consolidated 10-K total |
| State-regulated electric & gas rate base (plan-base) | Southern Company | ~$60B | Q2 2025 IR plan-base; no consolidated 10-K total |
When you compare two utilities, normalise the label first. A Duke “regulated earnings base” and an FPL “regulatory capital employed” are comparable regulatory asset measures, not GAAP goodwill or enterprise value.
Stated Growth Rates
Management plans state rate-base CAGRs through the capex window. FY2025 plan figures:
| Company | Stated RB CAGR | Endpoint / context |
|---|---|---|
| Southern Company | 9% | Through 2030; $81B 2026–2030 capex plan |
| Duke Energy | ~9.6% | Through 2030; $103B 2026–2030 capex plan |
| NextEra FPL | ~10% (plan) | Long-term plan; ~8.1% actual YoY FY2025 ($73.5B vs $68.0B) |
| American Electric Power | ~10% | To ~$128B by 2030 |
| Sempra | 11% | To $97B by 2030 |
| Dominion Energy | 11.9% | To $85.7B by 2030 from $48.2B end-2025 |
Actual YoY growth can diverge from the plan in any year because of regulatory lag, project delays, and disallowed costs. Dominion’s 11.9% plan CAGR and Southern’s 9% sit at opposite ends of the large-cap band, which feeds directly into the regulated EPS build.
Mini-Example: From Base to Return
Take a hypothetical mid-size operating company, or opco (the regulated entity that actually owns the plant, as distinct from its parent holding company), with $40B rate base (inside the peer range), 50% equity ratio (near the 49.84% average authorised equity ratio in 2024 rate cases), and 9.5% allowed ROE (inside the ~9%–10% band this guide uses as a working range).
Return on the equity layer of rate base:
$40B × 50% × 9.5% = $1.9B regulated equity earnings
That is the mechanical link between the asset base and the earnings stream. O&M, depreciation, and financing costs sit in the full revenue requirement; the equity return is the piece equity investors own.
With 9% rate-base CAGR on the plan, the base compounds to roughly $43.6B in year one before any regulatory lag. Earned ROE can still print below allowed ROE in heavy capex years because new plant enters the base only after it is used and useful and approved in a rate case. That lag is why allowed and earned ROE diverge.
What Rate Base Is Not
Rate base is not market capitalisation. NextEra traded at roughly $178B (10 Jun 2026) against FPL regulatory capital employed of $73.5B, because the parent holding company, or holdco, includes NextEra Energy Resources and because equity multiples capitalise EPS growth, credit headroom, and non-regulated optionality.
It is not a GAAP asset total either: goodwill, cash, and non-regulated subsidiaries sit outside the jurisdictional base unless a commission explicitly includes them.
What Matters Most
Pull the filed base and the stated CAGR from the issuer’s regulatory summary or IR deck before you model EPS. Label differences are cosmetic; the dollar bases and plan growth rates in the table above are the inputs that feed the regulated utility EPS build.
Regulated Utilities Sector Primer
Earned net income less the growth in regulated equity capital drives the free-cash-flow-to-equity build, priced off rate base and allowed ROE, screened against payout, P/E and FFO-to-debt.
The Excel model is the primer's two archetype builds live across 13 sheets: free cash flow to equity, earned net income less the increase in the regulated equity book, discounted at the cost of equity, on rate base, equity ratio and allowed ROE, with the rate-base roll-forward, the FFO-to-debt headroom screen and the funding plan on their own sheets. Change the rate-base growth, the allowed ROE or the cost of equity and the value per share moves; the credit and funding sheets update alongside it.
Frequently Asked Questions
- What is utility rate base?
- Rate base is net investment in plant and assets used and useful in providing service, on which regulators allow a fair return. NARUC defines it as investor-funded plant in service earning that return. It is the asset base that drives the revenue requirement in a cost-of-service rate case.
- Why do utilities use different names for rate base?
- Filers label the same regulatory concept differently. NextEra's FPL reports regulatory capital employed; Duke Energy reports a regulated earnings base; Dominion and Sempra use rate base; AEP publishes segment rate-base proxies that sum to a derived consolidated total. The labels differ; the economic idea is the same net plant earning an allowed return.
- How fast is US utility rate base growing?
- FY2025 plan CAGRs span roughly 9% to 11.9% through 2030 among large-cap names: Southern Company 9%, Duke Energy ~9.6%, NextEra FPL ~10%, American Electric Power ~10%, Sempra 11%, Dominion Energy 11.9%. Actual YoY growth can lag the plan in any given year because of regulatory timing and project in-service dates.
- How does rate base relate to earnings?
- Regulators set a revenue requirement as return on rate base plus operating expenses and depreciation. The equity portion of that return is rate base times the authorised equity ratio times allowed ROE. Faster rate-base growth, holding ROE and capital structure steady, is the primary driver of regulated EPS growth at wires-and-poles utilities.