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

How to invoice as a civil / mechanical / electrical engineer (pe) in Washington: WA sales tax 6.50% (applies to services), late fees capped at 1.5%/mo under Wash. Rev. Code §19.52.020. Step-by-step guide with a free template.

State sales tax
6.5%
Late fee cap
1.5%/mo
Net terms
30 days
Deposit
25%
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1. Washington-specific invoice requirements

  • Sales tax line: 6.50% state rate. Services billed to WA customers must include sales tax. State 6.5%; many services taxable. Combined commonly 8.5-10.5%.
  • Late-fee cap: Washington statute Wash. Rev. Code §19.52.020 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.
  • Right-to-cancel notice: Customers in Washington 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 Washington 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 Washington

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. Washington customers expect digital payment options today — accepting card and ACH typically reduces days-to-paid by 30–50%.

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

Washington metro guides

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

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