Which calculation to use when, what each one asks of you, and how TrueLoad runs both without making you choose up front.
The highest demand the home actually reached over the qualifying period, taken at 125%, plus the proposed new load. Because it replaces an estimate with a measurement, it is usually the lowest defensible number available: peer-reviewed research across nearly 12,000 homes found it roughly 40% lower than the traditional method on average.
The code's existing-dwelling calculation: general lighting from floor area, the small-appliance and laundry circuits, and every fastened-in-place appliance at nameplate, with the section's demand percentages applied. Enter the home and get the number in minutes.
Measured demand is the reason TrueLoad exists. It is the number that keeps a 100 A service off the upgrade list, and the one inspectors find hardest to argue with. But it needs the data, and smart meters are going in utility by utility and town by town, so one job has a year of interval history and the next has none.
That is why the same TrueLoad project also runs the traditional calculation. It makes TrueLoad usable anywhere in the US, including places with no access to interval data at all. You don't need a second tool for the homes without data, and you don't have to know which method a job will need before you open it. Use the data when it's there. Run the code's method when it isn't. Hand the inspector the same kind of report either way.
The code is estimating when it no longer has to.
Traditional demand factors are population averages, calibrated decades ago against a housing stock whose biggest loads were a range and a dryer. They do serious work, but they can't see what one particular house does. Its meter can.
Both paths share the same project, the same equipment schedule for the proposed new loads, and the same report workflow.
| Measured demand | Traditional calculation | |
|---|---|---|
| NEC method | The measured-demand method for existing installations | The optional method for existing dwelling units |
| The existing load comes from | The home's highest metered demand, at 125% | Floor area, circuit counts and the appliance inventory, with the section's demand factors |
| Utility data | 12 months, or the 30-day exception | None |
| What you enter about the home | The service itself | Floor area, circuits and appliances |
| Homeowner involvement | Usually, to authorize the data release | None |
| Time to a result | When the data arrives | Minutes |
| Applies to | Any existing service | A dwelling unit on a 3-wire 120/240 V or 120/208 V service |
| Typical result | Usually the lowest defensible number | The code's estimate |
| On the report | The full measured-demand calculation, the data summary and the methodology notes | The full worksheet line by line, with citations, your elections and your inventory attestation |
Every TrueLoad project can run either method, or both. The measured path works exactly as it always has, and the traditional path sits one click away from it.
From the utility you select on the project. A utility that provides interval data gets a measured-demand recommendation. One that doesn't yet gets the traditional calc. Both stay available either way.
Two tabs on the Existing Load step. Choosing one path never removes what's in the other, and your choice is remembered as you move through the project.
Data requests take time. Run the traditional calc today. If it passes, you're done. If it doesn't, the measured number is on its way, and it is usually the lower one.
When both are complete, the Results tab lists each method's calculated demand, margin and PASS or FAIL, including any that fail. You choose the report basis, and switching it is one click and free.
The traditional method is only as good as the appliance list. Where measured data exists, TrueLoad compares the metered peak with the connected load you entered, because a house cannot draw more than it has. An inventory that is almost certainly missing loads gets flagged.
The report carries the basis you chose, with its full worksheet. Include the methods comparison only when the method choice itself is being questioned: the report then shows every method that ran, each computed in full under its own rules and none blended, with the code reference that permits alternative methods.
No. Every plan includes both methods, and so does the free first project. A traditional-only project needs no utility data to unlock its results.
No, and TrueLoad will say so rather than print a report citing a section that doesn't govern the job. The traditional method covers a dwelling unit on a 3-wire 120/240 V or 120/208 V service. Measured demand has none of those restrictions, so that is the path for everything else. A whole building can also be evaluated one unit at a time.
Run the traditional calc now and tell TrueLoad which utility you need; every request goes onto our outreach list. If the customer can export an interval file from the utility's own portal, upload it. The project can re-run through measured demand whenever data becomes available.
Change them. On the traditional path under the 2020 and 2023 editions, you can restate the first-tier size, the tier and remainder percentages, and how EV charging is treated. Anything you change recalculates immediately and prints on the report as a preparer-stated election beside the section's own values, never as the code's numbers. Under the 2026 edition the table's percentages are code text and stay as written.
Your first project is free, on either path. No credit card required.