Why the Advertised Rate Is Not Your Rate
Every Texas retail electricity provider (REP) is required to publish an Energy Facts Label (EFL). The EFL lists an average price per kilowatt-hour at three usage benchmarks: 500 kWh, 1,000 kWh, and 2,000 kWh per month. Most providers advertise the 2,000 kWh figure because it is the lowest of the three. Most Texas households do not use 2,000 kWh every month. That mismatch is where billing confusion begins.
Learning to calculate electricity price yourself closes that gap. The math is not complicated. It requires four inputs and about five minutes. What it produces is a personalized estimate that reflects your actual usage, not a benchmark chosen by a marketing department.
The Electricity Cost Calculator Formula
The core electricity cost calculator formula for a Texas residential bill looks like this:
Monthly Bill = (Energy Charge x kWh Used) + Base Charge + TDU Delivery Charge + Taxes and Fees
Breaking each term down:
- Energy Charge: The variable rate in cents per kWh. This is what providers advertise. It may be flat or tiered.
- Base Charge: A fixed monthly fee that applies regardless of usage. Some plans charge zero; others charge $5 to $10. This fee is frequently buried in the EFL fine print.
- TDU Delivery Charge: The fee from your local transmission and distribution utility (Oncor, CenterPoint, AEP Texas, or TNMP, depending on your address). This has two parts: a fixed monthly charge and a per-kWh charge. Both are pass-throughs. Your REP does not set them, but your REP does collect them.
- Taxes and Fees: State sales tax (6.25% on the taxable portion), plus any local franchise fees (typically 0% to 2% depending on your city).
The EFL is required to disclose all of these. The advertised price per kWh at 1,000 kWh or 2,000 kWh is the all-in average, meaning it is supposed to fold in the base charge and TDU charges at that specific usage level. The problem is that the all-in average is only accurate at exactly that usage level. Use more or less, and your effective rate shifts.
How to Calculate kWh Cost: A Step-by-Step Example
Assume a household in Oncor territory (Dallas-Fort Worth area) using 900 kWh in a given month. The plan they are evaluating has:
- Energy charge: 9.8 cents per kWh (flat rate)
- Base charge: $9.95 per month
- Oncor TDU delivery: $3.42 fixed + 3.8138 cents per kWh (these are published Oncor tariff figures as of the most recent tariff filing; verify against the current Oncor schedule before budgeting)
- Texas sales tax: 6.25%
Step 1: Calculate the energy charge.
900 kWh x $0.098 = $88.20
Step 2: Add the base charge.
$88.20 + $9.95 = $98.15
Step 3: Add TDU delivery charges.
Fixed TDU: $3.42 Variable TDU: 900 kWh x $0.038138 = $34.32 Total TDU: $3.42 + $34.32 = $37.74
Running total: $98.15 + $37.74 = $135.89
Step 4: Apply sales tax.
$135.89 x 1.0625 = $144.38
Step 5: Calculate the effective rate.
$144.38 / 900 kWh = 16.04 cents per kWh (all-in effective rate)
The plan advertised a 2,000 kWh average rate, which likely sits around 13 to 14 cents per kWh at that usage level. At 900 kWh, the same plan costs 16.04 cents per kWh all-in. That is not a billing error. That is arithmetic. The base charge and fixed TDU charge spread across fewer kilowatt-hours produce a higher per-unit cost.
This is exactly why calculating electricity price at your actual usage tier matters.
Tiered and Bill Credit Plans: A Different Formula
Some Texas plans use a tiered energy rate or a bill credit structure. Both require a modified approach.
Tiered rates charge one rate up to a threshold and a different rate above it. Example:
- Tier 1: 8.5 cents per kWh for the first 1,000 kWh
- Tier 2: 11.2 cents per kWh for every kWh above 1,000
For a household using 1,400 kWh:
Tier 1: 1,000 x $0.085 = $85.00 Tier 2: 400 x $0.112 = $44.80 Total energy charge: $129.80
Then add base charge, TDU, and tax as before.
Bill credit plans work differently. The provider charges a single per-kWh rate across all usage but applies a credit (typically $30 to $60) if your usage lands within a specified band, often 1,000 to 2,000 kWh. Use outside that band and the credit disappears. The formula becomes:
Monthly Bill = (Energy Charge x kWh) + Base Charge + TDU + Taxes - Bill Credit (if applicable)
For a household using 900 kWh on a plan with a $50 credit that triggers only between 1,000 and 2,000 kWh, the credit does not apply. The EFL will show an attractive average rate at 1,000 or 2,000 kWh precisely because the credit is factored in. At 900 kWh, that same household pays full freight with no offset. The effective rate at 900 kWh will be materially higher than the advertised figure.
LightCompanies flags bill credit plans as higher-risk for households with variable seasonal usage. If your summer bills spike and your spring bills drop, you may routinely miss the credit window.
The TDU Variable: Why It Differs by City
Many shoppers focus entirely on the REP energy charge and overlook TDU delivery costs. This is a significant omission. TDU charges typically represent 30% to 40% of the total all-in bill for a median Texas household.
The four major TDUs in Texas and their approximate current tariff structures (PUCT docket filings; verify against current posted tariffs before finalizing any estimate):
- Oncor (North and West Texas): Fixed charge approximately $3.42/month + variable approximately 3.81 cents/kWh
- CenterPoint (Houston area): Fixed charge approximately $5.17/month + variable approximately 4.09 cents/kWh
- AEP Texas (Central and South Texas): Fixed charge approximately $4.00/month + variable approximately 4.16 cents/kWh
- TNMP (parts of West Texas and Panhandle): Fixed charge approximately $7.85/month + variable approximately 2.71 cents/kWh
A household in CenterPoint territory will pay more in TDU charges than the same-usage household in Oncor territory, assuming identical REP plans. Any electricity cost calculator that does not ask for your zip code or TDU is producing an incomplete estimate.
PUCT only publishes tariff snapshots quarterly. The figures above reflect the most recent available data. TDU rates do change, typically following a rate case before the PUCT.
Reading the EFL to Pull the Inputs You Need
The EFL is a standardized one-page document. Texas law requires REPs to make it available before contract signing. Here is where to find each input for the formula:
- Energy charge: Listed in the “Electricity Facts” section. For flat-rate plans, one number. For tiered plans, a table. For indexed plans, a reference index plus an adder.
- Base charge: Sometimes called a “monthly service charge” or “customer charge.” It is listed in the pricing section. If the EFL shows $0.00, verify this in the terms of service, because some providers embed a minimum bill charge that functions identically.
- TDU charges: Listed as a pass-through. The EFL will show the TDU fixed and variable components in a separate line.
- Taxes: Often shown as a percentage or folded into the all-in average rates at the three benchmark usage levels.
If any of these four items is missing from the EFL, the provider is out of compliance with PUCT disclosure rules. That is worth noting before signing.
Comparing Two Plans at Your Actual Usage Level
Once you can calculate electricity price for one plan, the comparison step is straightforward. Run the same formula for each plan you are evaluating, using the same kWh assumption for both. Do not compare the advertised rates directly. Compare the calculated totals.
Example: Two plans in Oncor territory for a household using 900 kWh.
Plan A:
- Energy charge: 9.8 cents/kWh, base charge $9.95
- Calculated all-in (from the earlier example): $144.38 = 16.04 cents/kWh effective
Plan B:
- Energy charge: 11.5 cents/kWh, base charge $0, bill credit of $40 for usage between 1,000 and 2,000 kWh
- Energy charge: 900 x $0.115 = $103.50
- No base charge: $0
- TDU: $37.74 (same Oncor territory)
- No credit applies at 900 kWh
- Pre-tax total: $103.50 + $37.74 = $141.24
- After tax: $141.24 x 1.0625 = $150.07 = 16.67 cents/kWh effective
Plan A is the lower-cost option at 900 kWh despite advertising a lower per-kWh rate on paper for Plan B. The absence of a base charge on Plan B does not offset the higher energy rate at this usage level. If that household’s usage rises to 1,500 kWh in summer, Plan B’s $40 credit activates and the calculus changes. Running the formula at multiple usage scenarios, say 700 kWh, 1,000 kWh, and 1,500 kWh, produces a fuller picture of which plan fits the household’s pattern.
Locating Your Usage History
The formula requires a kWh estimate. The most accurate source is your own history. Texas Smart Meters log interval data. Customers in most Texas service areas can access 12 to 24 months of hourly usage data through SmartMeterTexas.com at no charge. Download the monthly summary and use three figures:
- Your average monthly usage (for a baseline estimate)
- Your lowest-usage month (spring shoulder season, typically March or April)
- Your highest-usage month (peak summer, typically July or August)
Running the electricity cost calculator formula at all three gives a range rather than a single number. That range is more useful for plan selection than any single-point average.
What This Formula Does Not Cover
The formula above handles fixed-rate plans and simple tiered plans well. It is less precise for:
- Indexed or variable-rate plans, where the energy charge floats with a market index (ERCOT real-time or day-ahead prices). These require a probabilistic range, not a single estimate.
- Time-of-use (TOU) plans, where the rate changes by hour or by on-peak and off-peak windows. Calculating kWh cost for TOU plans requires usage data broken out by time block, not just total monthly kWh.
- Solar buyback plans, where exported kWh reduce the bill. The net calculation requires both import and export data.
Each of these plan types has its own calculation approach. LightCompanies covers each in separate supporting articles linked from the pillar page on Texas plan types.
The Takeaway
Calculating electricity price before signing a contract is not a specialist skill. It is four variables, one formula, and roughly five minutes per plan. The EFL provides all the inputs. SmartMeterTexas provides the usage history. A spreadsheet or a calculator handles the arithmetic.
The providers that benefit most from shoppers skipping this step are the ones whose plans look competitive at benchmark usage levels and expensive at actual usage levels. Running the numbers at your own usage tier is the single most effective way to avoid that outcome.