Economic nexus tracker in Excel with Copilot or ChatGPT for 5 US states
A remote seller has to register and collect sales or use tax in a state once its sales into that state pass the state's economic nexus threshold, and each state measures that threshold differently. California counts sales over $500,000 in the preceding or current calendar year, Texas looks at the previous 12 calendar months, New York requires both more than $500,000 and more than 100 sales over its own four sales tax quarters, Washington counts more than $100,000 in the current or prior year, and Illinois has used a single $100,000 test over a 12-month lookback since January 1, 2026.
A tracker in Excel turns those five different windows into one monthly control: sales by state go in once, each state's test runs against its own measurement period, and the sheet shows which thresholds are met, how much headroom is left and when registration or collection has to start. Copilot in Excel and ChatGPT can build most of that sheet from a prompt, but the thresholds themselves have to be typed in from the state revenue departments, and the AI output has to be checked against a result computed independently.
The worked example below uses an illustrative seller with sales into five states and an evaluation date of October 1, 2026. Two of the five tests are met (California and Washington), one fails only on the transaction count (New York), and two are below the threshold with very little headroom (Texas and Illinois).
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WHAT A SALES TAX NEXUS TRACKER HAS TO MEASURE.
Since the 2018 Wayfair decision, states have been able to require out-of-state sellers to collect tax based on sales volume alone, without offices, staff or inventory in the state. For a growing e-commerce or SaaS-adjacent business that ships physical goods, that means the list of states where it must register can change in any month, and a missed threshold usually surfaces later as uncollected tax the seller has to pay out of its own margin.
The tracker has three jobs. It aggregates gross sales, and where a state requires it the number of transactions, by destination state and month. It applies each state's own rule, which differs in the amount, in what counts as a sale, in the measurement window and in whether one or two conditions must be met. It turns a crossed threshold into a date by which registration or collection must begin. Income tax nexus for state corporate taxes follows different rules, covered in our article on state corporate income tax apportionment and nexus issues, and is outside the scope of this sheet.
The thresholds below were checked on each state revenue department's own pages on November 10, 2026. States amend these rules, as Illinois did for 2026, so the threshold table belongs on a separate input tab with the date of the last check next to it.
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State | Threshold | What counts | Measurement window |
California | More than $500,000 | Total sales of tangible personal property delivered into California, including related persons | Preceding or current calendar year |
Texas | Safe harbor while revenue is less than $500,000 | Gross revenue from taxable and nontaxable sales into Texas, including marketplace sales | Previous 12 calendar months |
New York | More than $500,000 AND more than 100 sales | Gross receipts and number of sales of tangible personal property delivered into New York | Immediately preceding four New York sales tax quarters |
Washington | More than $100,000 | Combined gross receipts, including exempt and marketplace sales | Current or prior year |
Illinois | $100,000 or more | Cumulative gross receipts from sales of tangible personal property to Illinois purchasers | 12-month lookback, evaluated quarterly |
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Three details in that table break simple trackers. New York's quarters run March to May, June to August, September to November and December to February, so a sum by calendar quarter gives the wrong window. Illinois dropped its 200-transaction test from January 1, 2026, and from quarters beginning after March 31, 2026 retailers determine on a rolling quarterly basis whether they meet the $100,000 test. Texas states its rule as a safe harbor, so the question is whether revenue stays below $500,000 rather than whether it exceeds it.
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COPILOT IN EXCEL AND CHATGPT: DOCUMENTED REQUIREMENTS AND LIMITS.
Both tools can produce the formulas and the summary, but they work in different places. Copilot in Excel edits the workbook itself, while ChatGPT analyzes an uploaded file in a separate Python environment and returns results or files from there. The requirements below are taken from Microsoft's and OpenAI's support documentation as published on November 10, 2026.
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Item | Copilot in Excel | ChatGPT data analysis |
Plans | Microsoft 365 Personal or Family with an AI credits plan, Microsoft 365 Premium, a commercial Microsoft Copilot subscription, or an eligible business or enterprise subscription | File uploads available to Plus and Enterprise users; Free users limited to 3 files per day |
Where it works | Inside the workbook, in edit, plan and chat modes on Windows, Mac and the web | In an isolated Python environment using pandas |
File limits | Strict Open XML files not supported; editing requires Calculation Options set to Automatic | 512 MB per file; spreadsheets about 50 MB depending on row size; up to 10 files per conversation |
Network | Can fetch web information | Code environment cannot make outbound network requests |
Vendor caution | Output can contain mistakes; review before relying on it | Environment destroyed within 13 hours of inactivity |
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Microsoft's own FAQ for Copilot in Excel advises against relying on Copilot for decisions in finance, legal or medical matters and asks users to review and verify what it creates. That caution applies directly to nexus thresholds. Copilot can fetch web information, and a chatbot may answer from older training data, so neither should be the source of the threshold values. The safer design keeps the thresholds in a typed input table that a person maintains from the state websites and asks the AI only to build the arithmetic around it.
Data handling also differs. In Excel, saved Copilot changes are visible to anyone with access to the file, including coauthors, and Copilot activity history can be deleted from the pane. ChatGPT keeps uploaded files for the retention period of the chat, and OpenAI states that deleted content is removed from its systems within 30 days. A sales ledger by customer and address is personal data in many cases, so for the ChatGPT route an export aggregated by state and month, without customer names or addresses, is the better input.
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THE ILLUSTRATIVE SALES DATA FOR THE NEXUS TEST.
The illustrative seller ships physical goods from a single warehouse in Delaware and sells through its own website and a marketplace. The table shows gross sales delivered into each of the five states, all channels and exempt sales included, with New York's order count in a separate column. January to August 2025 are aggregated in one row because only the calendar-year tests for California and Washington need them. These figures are illustrative and do not describe any real company.
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Month | CA sales | TX sales | NY sales | NY orders | WA sales | IL sales |
Jan-Aug 2025 | 312,000 | 268,000 | 301,000 | 51 | 58,300 | 51,200 |
Sep 2025 | 38,500 | 35,900 | 43,800 | 7 | 8,100 | 7,100 |
Oct 2025 | 41,200 | 38,200 | 44,100 | 7 | 9,300 | 7,400 |
Nov 2025 | 44,800 | 40,100 | 45,600 | 8 | 10,400 | 7,900 |
Dec 2025 | 52,600 | 47,600 | 51,200 | 9 | 10,200 | 8,600 |
Jan 2026 | 46,100 | 37,400 | 42,300 | 7 | 11,500 | 7,800 |
Feb 2026 | 47,300 | 38,800 | 43,000 | 7 | 11,900 | 8,100 |
Mar 2026 | 52,900 | 39,500 | 44,900 | 8 | 12,400 | 8,300 |
Apr 2026 | 55,200 | 40,200 | 45,200 | 8 | 12,600 | 8,400 |
May 2026 | 58,400 | 41,000 | 46,700 | 8 | 13,100 | 8,600 |
Jun 2026 | 60,700 | 41,700 | 47,100 | 8 | 13,800 | 8,700 |
Jul 2026 | 61,800 | 40,900 | 47,800 | 8 | 14,200 | 8,500 |
Aug 2026 | 63,100 | 41,600 | 48,400 | 8 | 14,600 | 8,400 |
Sep 2026 | 64,300 | 41,300 | 49,100 | 9 | 9,900 | 8,700 |
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In the workbook the same data sits better in long format, one row per state and month, in an Excel table named tblSales with the columns Date (the last day of each month), State, Sales and Orders. An evaluation date in a named cell called EvalDate, here October 1, 2026, drives every window, and a second named cell, NYQEnd, holds the end of the last complete New York quarter, here August 31, 2026.
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PROMPTS AND FORMULAS FOR THE NEXUS TRACKER IN EXCEL.
The first prompt goes to Copilot in Excel in edit or plan mode, with tblSales and a threshold table named tblRules on the sheet. Plan mode lets the reviewer read the steps before Copilot changes anything.
Using tblSales (Date, State, Sales, Orders) and tblRules (State, Amount, Window, CountTest),
add a sheet called Nexus Test with one row per state. For each state calculate sales in the
window stated in tblRules relative to the date in EvalDate: CA and WA use calendar 2025 and
calendar 2026 to date; TX and IL use the 12 months ending the month before EvalDate; NY uses
the 12 months ending on NYQEnd and also sums Orders. Add columns for threshold met (Yes/No),
headroom in dollars, and the formula used. Do not type any threshold amounts yourself; read
them from tblRules. Do not change tblSales or tblRules.The core of what Copilot should produce is a set of SUMIFS formulas with date conditions. Writing the expected formulas down before running the prompt makes the review faster, because the reviewer compares structure rather than reading Copilot's output from scratch.
TX and IL, previous 12 calendar months:
=SUMIFS(tblSales[Sales],tblSales[State],"TX",tblSales[Date],">"&EOMONTH(EvalDate,-13),tblSales[Date],"<="&EOMONTH(EvalDate,-1))
CA and WA, current calendar year to date:
=SUMIFS(tblSales[Sales],tblSales[State],"CA",tblSales[Date],">="&DATE(YEAR(EvalDate),1,1),tblSales[Date],"<"&EvalDate)
NY, four New York quarters ending on NYQEnd (sales; repeat with tblSales[Orders] for the count):
=SUMIFS(tblSales[Sales],tblSales[State],"NY",tblSales[Date],">="&EDATE(NYQEnd+1,-12),tblSales[Date],"<="&NYQEnd)
NY test, both conditions:
=IF(AND(NY_Sales>500000,NY_Orders>100),"Yes","No")For ChatGPT, the input is a CSV export of the same long table, aggregated by state and month. The prompt asks for the calculation and for the intermediate sums, so each figure can be traced.
Attached is monthly sales by destination state (columns: Date, State, Sales, Orders).
Evaluation date: 2026-10-01. Apply these rules exactly as written and show the sum for each window:
CA: total sales > 500,000 in calendar 2025 or in calendar 2026 to date.
TX: safe harbor while sales in the 12 months Oct 2025-Sep 2026 are below 500,000.
NY: sales > 500,000 AND orders > 100 in Sep 2025-Aug 2026.
WA: sales > 100,000 in calendar 2025 or calendar 2026 to date; give the month the 2026 total first exceeds 100,000.
IL: sales >= 100,000 in Oct 2025-Sep 2026.
Return a table: state, window, sales, orders where relevant, threshold, met yes/no, headroom.··········
EXPECTED RESULT OF THE NEXUS TEST, COMPUTED INDEPENDENTLY.
The figures below were computed in Python from the illustrative table. An AI-built tracker that returns anything different has a window or a condition wrong, and the difference usually points to which one.
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State | Window | Sales | Threshold | Met | Headroom or excess |
California | Calendar 2025 | 489,100 | More than 500,000 | No | 10,900 below |
California | Jan-Sep 2026 | 509,800 | More than 500,000 | Yes | 9,800 over |
Texas | Oct 2025-Sep 2026 | 488,300 | Below 500,000 for safe harbor | No | 11,700 below |
New York | Sep 2025-Aug 2026 | 550,100 and 93 orders | More than 500,000 and more than 100 | No | 8 orders short |
Washington | Calendar 2025 | 96,300 | More than 100,000 | No | 3,700 below |
Washington | Jan-Sep 2026 | 114,000 | More than 100,000 | Yes | 14,000 over |
Illinois | Oct 2025-Sep 2026 | 99,400 | 100,000 or more | No | 600 below |
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California's 2026 sales passed $500,000 in September, when the year-to-date total went from 445,500 to 509,800. The seller now meets the California test for the current calendar year and has to register with the California Department of Tax and Fee Administration and collect use tax. The CDTFA general information page does not set out a separate deadline after the threshold is crossed, so the date of registration is a question to settle with CDTFA directly rather than one the tracker can answer.
Washington's 2026 total passed $100,000 in August, moving from 89,500 at the end of July to 104,100. Washington's rule is that a seller who did not meet the threshold in the prior year begins collecting on the first day of the month that starts at least 30 days after meeting it. With monthly data the tracker knows only the month, and the exact day changes the answer. If the threshold was crossed on August 1 or 2, 2026, collection starts September 1, 2026, and if it was crossed on any day from August 3 to August 31, it starts October 1, 2026. Invoice-level data for August pins the date.
New York shows why the AND test needs its own column. Gross receipts of 550,100 are well above $500,000, but 93 sales are below the 100-sale condition, so the seller is not required to register on the lookback ending August 31, 2026. The next review comes after the New York quarter ending November 30, 2026, and once both conditions are met New York requires a certificate of registration within 30 days and collection 20 days after that.
Texas and Illinois are both below their thresholds with headroom of 11,700 and 600. The next Illinois evaluation, for the 12 months ending December 31, 2026, drops October to December 2025 (23,900 in total) and adds the same months of 2026, so the threshold is met if those three months bring in at least 24,500. A tracker that still applied the old 200-transaction test would add nothing for Illinois from 2026, because the only remaining test is the $100,000 of gross receipts.
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WHERE AI-BUILT NEXUS TRACKERS GO WRONG AND HOW TO CHECK THEM.
The most frequent error is the window. Copilot and ChatGPT both tend to default to calendar quarters or calendar years, which is wrong for New York and for the rolling 12-month tests in Texas and Illinois. Checking the start and end dates of every SUMIFS against the threshold table catches this quickly, and the expected formulas above serve as the reference.
The second error is the comparison operator. California, New York and Washington test for more than the amount, Illinois for the amount or more, and Texas grants its safe harbor while revenue is less than $500,000. A tracker that uses greater-or-equal everywhere gives the wrong answer only at the exact threshold, which is rare, but the formulas should still match the wording of each state's rule.
The third error is the base. Texas and Washington both include marketplace sales, Washington also includes exempt sales, and California counts sales by related persons. An export that only includes taxable sales from the seller's own website understates all three. The same discipline applies to any AI-generated workbook, and our guide on auditing and explaining Excel formulas with Copilot, Claude or ChatGPT covers how to trace each formula back to its inputs.
Three items stay with a person and should not be delegated to the AI. Threshold values and windows are updated from the state revenue department pages, with the date of the check recorded. The decision to register, and the registration itself, is made by the tax owner after reviewing the result. A crossed threshold triggers a review of exposure for sales made before collection began, which may involve the state's voluntary disclosure procedures and professional tax advice.
The tracker fits naturally into the monthly close. Running it after sales are closed for the month, alongside the other close checks described in our month-end close checklist with Copilot, Claude and ChatGPT, means a threshold crossed in one month is flagged within days rather than at year end. Vendor compliance runs on a similar annual cycle, and the $2,000 reporting threshold for 2026 is covered in our article on Form 1099-NEC and 1099-MISC.
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ECONOMIC NEXUS TRACKING IN EXCEL: WHAT THE FIVE TESTS SHOW.
For the illustrative seller on October 1, 2026, California and Washington thresholds are met, New York fails only on the number of sales, and Texas and Illinois sit just below their thresholds. Each result depends on a different window, and three of the five would come out wrong in a tracker that summed by calendar quarter or applied a single greater-or-equal test.
Copilot in Excel and ChatGPT can build the SUMIFS logic, the summary table and the headroom columns in minutes, and both vendors' documentation tells users to verify the output before relying on it. The parts that decide the outcome are the threshold table maintained from state sources, a sales base that includes marketplace and exempt sales where the state counts them, and the exact crossing date for states like Washington that set collection start dates by day. Those remain the controller's responsibility, and the independently computed result is the check that the AI's arithmetic matches the rules.
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