Texas Electricity Plan Comparison Methodology
By the TexasPowerCost Editorial Team — independent Texas electricity analysis · Last reviewed October 18, 2026 · how we analyze plans
Last updated: October 18, 2026 · 8 min read
The official Texas plan-shopping portal, Power to Choose, sorts plans by the advertised price at 1,000 kWh. That's a single point on a multi-point pricing curve. Real households almost never use exactly 1,000 kWh in a month — so the "cheapest" plan on Power to Choose is rarely the cheapest plan for a real bill. This page documents exactly how TexasPowerCost.com solves the problem, so you can verify every number on the site.
The short answer
TexasPowerCost compares plans by computing the true monthly bill at your actual usage. We use linear interpolation across the three EFL price points (500, 1,000, 2,000 kWh), add current TDU delivery charges and base fees, and sort by total dollar bill — not by advertised per-kWh rate.
The Problem With Sorting by Advertised Rate
Every Texas electricity plan publishes an Electricity Facts Label that lists the average per-kWh price at exactly three usage levels: 500, 1,000, and 2,000 kWh. Providers design plan structures — bill credits, minimum-usage fees, tier breaks — to optimize the 1,000 kWh figure because that's the number Power to Choose sorts by. A plan can quote 8¢/kWh at 1,000 kWh while charging an effective 14¢/kWh at 800 kWh because of a bill credit that doesn't trigger below 1,000.
For a real household, the consequence is that ranking plans by the 1,000 kWh advertised rate routinely puts the most expensive real plan at the top of the list. This is the structural problem TexasPowerCost.com is built to solve.
The Linear Interpolation Method
A Texas EFL gives three (usage, price) data points. Given these, the price at any in-between usage level can be estimated by drawing a straight line between the relevant pair of points. The algorithm:
If usage is at or below 500 kWh, use the 500 kWh price. If usage is between 500 and 1,000 kWh, interpolate linearly between the 500 and 1,000 kWh prices. If usage is between 1,000 and 2,000 kWh, interpolate between the 1,000 and 2,000 kWh prices. If usage exceeds 2,000 kWh, use the 2,000 kWh price.
The math: interpolating to 1,250 kWh
- EFL gives: 9.2¢/kWh at 1,000 kWh and 11.4¢/kWh at 2,000 kWh.
- Real usage: 1,250 kWh.
- Interpolated rate: 9.2 + (1,250 - 1,000) × (11.4 - 9.2) / 1,000 = 9.75¢/kWh.
- Estimated energy charge: 1,250 × 9.75¢ = $121.88.
- Add TDU charges and base fees → real total bill.
This is a deliberately simple model. It matches how providers themselves construct the EFL — they pick three points on what is essentially a piecewise-linear curve — so the interpolated rate is a faithful estimate of what the plan would actually charge at the in-between usage level. No other major Texas plan-comparison site uses this method as the default. Most show only the headline 1,000 kWh rate.
How TDU Charges Are Folded In
Two structural facts make TDU inclusion essential. First, each TDU (Oncor, CenterPoint, AEP Texas, TNMP) has a different delivery charge schedule. Second, plans are filed in one of two formats — energy-only or all-inclusive — and the EFL discloses which approach is used. To compare across plans fairly, TexasPowerCost normalizes both formats to a single all-in monthly cost by adding the current PUCT-approved TDU tariff to every energy-only plan in the comparison.
TDU tariffs change on March 1 and September 1. The site pulls the current rates from the PUCT-approved tariff filings, so comparisons reflect what you'll actually be billed — not what last year's filing said.
How Bill Credits and Minimum-Usage Fees Are Applied
Bill credits in Texas typically take the form of a flat dollar amount applied when monthly usage falls inside a specific kWh range. The comparison engine reads the credit structure from each plan's EFL and applies it only when your usage actually qualifies. Plans that lose their credit at your usage level are ranked accordingly — usually well down the list — even if their headline 1,000 kWh rate is among the lowest.
Minimum-usage fees work in the opposite direction. A plan may impose a $9 or $13 monthly fee if usage falls below a threshold like 800 or 1,000 kWh. The fee is added to the bill estimate for users whose usage falls below the threshold, so those plans show their real cost rather than a misleadingly low rate.
Data Sources and Refresh Cadence
| Data | Source | Refresh |
|---|---|---|
| Plan rates (EFL) | Power to Choose API (PUCT) | Daily, rotating ZIP schedule |
| TDU delivery charges | PUCT-approved tariff filings | Bi-annual + ad hoc |
| Provider company data | Power to Choose API | Synced with plan data |
| ZIP-to-TDU mapping | PUCT service-territory map | Quarterly |
Limitations of the Method
Linear interpolation is a strong fit for most Texas plans because the EFL itself is constructed by sampling three points on a piecewise-linear pricing structure. The method becomes less accurate for plans with non-linear features — tiered plans with sharp cliffs, free-nights plans with rate changes by hour-of-day, or indexed-rate plans whose underlying benchmark moves. For these plan types, the calculator shows an estimate plus a note about additional uncertainty.
Watch out
Linear interpolation gives you a reliable estimate for fixed-rate flat plans. For time-of-use plans (free nights, free weekends), your real bill depends heavily on what hours you actually use power. Run the comparison and then verify against your interval data from Smart Meter Texas if you're considering a TOU plan.
How to Verify the Numbers Yourself
The methodology is transparent. Every plan page on the site shows the EFL price points the calculation is built from, the TDU delivery charges added, and the final all-in monthly bill. You can take the EFL number from the official PUCT Power to Choose page, apply the same linear interpolation manually, and verify the result. The True Cost Calculator exposes each step.
The Texas-Specific Bottom Line
TexasPowerCost's comparison engine produces a real estimate of your monthly bill by interpolating across the three EFL price points, including current TDU delivery charges, and applying any bill credits or minimum-usage fees at your actual usage level. Plans are sorted by total dollar bill rather than by advertised per-kWh rate. The method is simple, transparent, and structurally different from the official Power to Choose sort — which is why the cheapest plan on the two sites is frequently not the same plan.
See the methodology applied to your ZIP
Every plan in your area, ranked by real total bill at your actual usage.
Run My ZIP →Common Questions Texans Ask
How does TexasPowerCost compare Texas electricity plans?
TexasPowerCost pulls every plan from the official Power to Choose API for your specific ZIP, then linearly interpolates across the three EFL price points (500, 1,000, and 2,000 kWh) to estimate the per-kWh rate at your real usage level. The monthly figure shown for each plan is the energy-supply cost at that usage, including base charges and bill credits. Plans are sorted by that true monthly cost — not by the misleading 1,000 kWh advertised rate. The regulated TDU delivery charge is reported separately, because it is identical for every provider in your ZIP and therefore cannot change which plan is cheapest.
Why is the 1,000 kWh advertised rate misleading?
Because providers design plans to win the 1,000 kWh sort on Power to Choose. Bill credits, base charges, and tier breaks are engineered to crater the effective rate at exactly that point. A household using 800 kWh or 1,300 kWh routinely pays an effective rate 30% to 70% higher than the advertised number on the exact same plan.
What is linear interpolation in the EFL context?
It is a mathematical method for estimating a price at an in-between usage level given the prices at three known points. If the EFL shows 10¢/kWh at 500, 9¢/kWh at 1,000, and 11¢/kWh at 2,000, linear interpolation calculates the rate at 750 kWh by drawing a straight line between the 500 and 1,000 kWh points. Simple, transparent, and aligned with how EFLs are constructed.
Why doesn't Power to Choose use this method?
Power to Choose was built to display the data providers file, not to model individual household bills. It shows the three EFL price points and lets the user sort by one of them. The interpolation step is left to the consumer. TexasPowerCost performs the interpolation automatically so the displayed cost is a real estimate of your bill rather than a single data point on a curve.
Are TDU delivery charges included in the comparison?
They are reported, but deliberately kept out of the ranking. Each plan figure is the energy-supply cost — the portion you actually shop — and the current TDU delivery charge for your ZIP (the fixed monthly customer charge plus the per-kWh delivery rate) is shown alongside it, so city and ZIP pages also give an estimated all-in total. The ranking itself is computed on energy supply because the TDU charge is set by the PUCT and is identical for every retail provider in your ZIP: it changes what you pay, never which plan is cheapest.
How fresh is the plan data?
Plan data syncs from the Power to Choose API daily on a rotating ZIP schedule. The "Last updated" timestamp on every city, ZIP, and plan page shows the actual freshness for that specific data set. Most ZIPs are refreshed at least every few days, and the largest cities are refreshed daily.
Does the comparison account for seasonal usage swings?
The default uses an annualized average usage profile, but the calculator and search tools accept any specific kWh figure. For households with large seasonal swings — common in Texas — the right approach is to run the search twice, once at the summer peak and once at the winter low, then pick a plan that prices reasonably at both extremes.
Is the methodology open or auditable?
The methodology is intentionally transparent. Every plan page shows the EFL price points the calculation uses, the interpolated rate at your usage, and the resulting monthly energy-supply cost, with the regulated TDU delivery charge stated separately. You can verify the math by hand against the official PUCT EFL.
Your Next Move
To see the methodology applied to your ZIP, run a search on the homepage. The True Cost Calculator exposes the interpolation step by step. For the structural reason the 1,000 kWh rate misleads, see every Texas electricity plan type, explained. To understand how the plan layer combines with the delivery layer, see Texas TDU delivery charges, fully explained.