How to Invoice as a Civil / Mechanical / Electrical Engineer (PE) in Illinois

How to invoice as a civil / mechanical / electrical engineer (pe) in Illinois: IL sales tax 6.25% (services usually exempt), late fees capped at 1.5%/mo under 815 ILCS 205/4 (Interest Act), written contracts required over $1,000. Step-by-step guide with a free template.

State sales tax
6.25%
Late fee cap
1.5%/mo
Net terms
30 days
Deposit
25%
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1. Illinois-specific invoice requirements

  • Sales tax line: 6.25% state rate. Most services rendered in Illinois are exempt from sales tax — but materials, parts, and tangible goods are not. Services largely exempt; combined rates up to ~11% in Chicago.
  • Late-fee cap: Illinois statute 815 ILCS 205/4 (Interest Act) caps interest on unpaid invoices at 1.5% per month. Spell out the rate in writing on every invoice and in your contract — courts won't enforce undisclosed fees.
  • Written contract required: Illinois requires a signed agreement for any job over $1,000. Reference the contract number on the invoice.
  • Right-to-cancel notice: Customers in Illinois get 72-hour cancellation rights on certain home-services contracts. Disclose this in your terms.

2. Civil / Mechanical / Electrical Engineer (PE) line items + standard terms

Every civil / mechanical / electrical engineer (pe) invoice in Illinois should itemize work clearly. Standard civil / mechanical / electrical engineer (pe)s use Net 30 terms with a 25% deposit required upfront.

  • Project fee — billed by flat.
  • Hourly engineering — billed by hour (~$175 default).
  • PE stamp & sealing — billed by flat.
  • Site visit — billed by flat.

3. Civil / Mechanical / Electrical Engineer (PE) licensing in Illinois

PE license required to stamp drawings or sign engineering opinions. Discipline-specific rules apply.

4. Send and follow up

Send the invoice the same day work completes. Use software that records open events and offers a one-click online payment so you don't need to chase a check by mail. Illinois customers expect digital payment options today — accepting card and ACH typically reduces days-to-paid by 30–50%.

Average invoice
$6,500
State
IL
Net terms
30 days
Deposit
25%

Illinois metro guides

Metro-specific guides include the combined sales-tax rate and local pricing benchmarks.

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