How to Write an Invoice in 4 Steps | Projul

Invoicing is a fundamental aspect of any business operation, playing a critical role in managing cash flow and maintaining professional relationships with clients. A well-structured invoice not only ensures timely payments but also reflects the professionalism of your business. Yet most contractors treat invoicing like an afterthought, something they get around to on Friday afternoon if they remember.

That approach is costing you money. Slow invoicing means slow payments, and slow payments mean cash flow problems. Here’s a straightforward guide on how to write an effective invoice in just four steps, plus the common mistakes that delay payment and how to avoid them. For a deeper dive, see our complete guide to contractor invoicing.

Step 1: Choose the Right Tool

Before you write a single invoice, decide how you’re going to create and send them. Your options range from free to fully automated, and the tool you choose directly affects how fast you get paid.

Paper and Word Documents

Some contractors still write invoices on carbon copy pads or type them into a Word template. This works for occasional one-off jobs, but it falls apart fast. Paper invoices get lost in truck cabs, have math errors, and offer no way to track whether the client even received them. If a client says “I never got your invoice,” you have no way to prove otherwise.

Spreadsheets

A step up from paper. You can build a template in Excel or Google Sheets with formulas that calculate totals and taxes automatically. But you’re still manually entering every line item, and the invoice lives on your computer or in a folder somewhere. If your hard drive dies, your invoicing history goes with it.

Invoicing Software

This is where most contractors should be. Projul’s invoicing software creates invoices straight from your estimate with one click. All the line items, quantities, and pricing carry over automatically. No copying numbers, no re-entering data, no math errors. The invoice is digital, trackable, and includes built-in payment processing so the client can pay immediately.

The time difference is significant. What takes 30-45 minutes with a spreadsheet takes about 2 minutes with invoicing software. Multiply that by 20 invoices a month, and you’re saving 10+ hours of admin time every month. That’s time you could spend on the job site or bidding new work.

What About QuickBooks Invoicing?

QuickBooks has invoicing functionality, and it works fine for basic billing. But it doesn’t connect to your estimates, your job schedule, or your field operations. You end up entering the same information twice - once in your project management system and once in QuickBooks.

A better approach: create invoices in Projul (where they’re connected to your estimates and job costs), and let them sync to QuickBooks through Projul’s QuickBooks integration. Your bookkeeper sees the invoice in QuickBooks. Your project manager created it in Projul. Nobody entered anything twice.

Step 2: Include Essential Information

Every invoice needs complete business and client details to avoid payment delays. Missing information is the number one reason invoices get sent back or ignored. Here’s the full checklist:

Your Business Information

• Business name (legal name, not just your DBA)
• Physical address
• Phone number and email
• Logo (this is a small thing that makes a big difference in how professional your invoice looks)
• License number (required in many states)
• Tax ID or EIN (for commercial clients who need it for their records)

Client Information

• Client name (full legal name for commercial clients, or homeowner name for residential)
• Property address (especially important if the billing address is different from the job site)
• Contact email and phone

Invoice Details

• Invoice number. Use a sequential numbering system. INV-001, INV-002, etc. This makes tracking and referencing invoices simple. Projul assigns invoice numbers automatically so you never duplicate or skip a number.
• Invoice date. The date you’re issuing the invoice.
• Due date. When payment is expected. Be specific. “Due upon receipt” or “Net 30” are common terms. More on payment terms below.
• Project name or job number. Tie the invoice to a specific project so the client knows exactly what they’re paying for.

Description of Work

This is where many contractors get sloppy. “Labor and materials - $12,500” doesn’t tell the client anything. Be specific:

• “Demo and removal of existing kitchen cabinets and countertops”
• “Install 42 linear feet of custom maple cabinetry per approved plans”
• “Rough-in plumbing for kitchen island sink relocation”

When clients can see exactly what they’re paying for, they pay faster. Vague invoices invite questions, and every question adds days to your payment timeline.

Projul’s templates auto-fill your company details and pull line items directly from your approved estimate, so you never miss a field and you never have to retype a scope description.

Step 3: Calculate the Costs

Accurate cost calculations prevent disputes and build client trust. Here’s how to get this section right:

Line-Item Breakdown

List each service or product with its corresponding cost. For construction invoices, this typically means:

• Labor. Hours worked x rate, or a fixed amount per task. If you’re billing time and materials, include the dates worked and the number of hours each day.
• Materials. List specific materials with quantities and unit costs. “16 sheets 1/2” drywall @ $14.50/sheet = $232” is much better than “drywall - $232.”
• Equipment. Rental costs, fuel, or wear-and-tear charges for heavy equipment.
• Subcontractor costs. If you’re marking up sub costs, show the line item but you don’t need to show your markup percentage.

Taxes and Discounts

Apply any relevant taxes and note any discounts you’re offering. Tax rules vary by state and by type of work. In some states, labor is taxable. In others, only materials are taxed. Some states exempt certain types of construction work entirely. Know your state’s rules, or better yet, set them up once in your invoicing software and let it calculate automatically.

If you offered a discount (early payment, repeat customer, or multi-project deal), show it as a separate line item so the client sees the value.

Total Amount Due

State the total amount clearly at the bottom. Include a clear breakdown:

• Subtotal: $12,500
• Sales Tax (7.5%): $937.50
• Early Payment Discount (-2%): -$268.75
• Total Due: $13,168.75

Projul auto-calculates totals, taxes, and discounts from your estimate data. If you built a thorough estimate, your invoice calculations are done before you even create the invoice. This direct connection between estimating and invoicing is what keeps your job costing accurate. For more on tracking project finances, check out our complete guide to construction job costing.

Step 4: Set Up Payment Processing

Curious what other contractors think? Check out Projul reviews from real users.

The easier you make it for clients to pay, the faster you get paid. This is not complicated, but a lot of contractors still make it harder than it needs to be.

Payment Methods

Offer multiple ways to pay. At minimum:

• Credit card. Most homeowners prefer this. Yes, there are processing fees, but getting paid immediately is worth far more than the 2.5-3% fee. Some contractors pass the processing fee to the client (Projul supports this automatically).
• ACH / bank transfer. Lower fees than credit cards. Common for commercial clients and larger payments.
• Check. Still common, especially with older clients and commercial accounts. But checks add 5-10 days to your payment timeline (mailing time + deposit + clearing).

Built-in payment processing is the biggest advantage of using invoicing software. When a client receives a Projul invoice, they can click a button and pay right then. No writing a check, finding a stamp, or driving to the bank. The payment records in Projul and syncs to QuickBooks automatically.

Payment Terms

Your payment terms set expectations and give you legal standing if a client doesn’t pay. Include these on every invoice:

• Due date. “Net 15” (due in 15 days) or “Net 30” (due in 30 days). For residential work, “Due upon receipt” or “Net 7” is more common and appropriate.
• Late payment fees. “A 1.5% monthly finance charge will be applied to balances over 30 days past due.” Check your state’s laws on maximum allowable late fees.
• Deposit requirements. For larger projects, many contractors bill a deposit (25-50%) before work starts, progress payments at milestones, and a final payment at completion.

Progress Billing vs. Final Billing

For projects lasting more than a few days, don’t wait until the end to bill. Progress billing keeps cash flowing throughout the project and reduces your risk.

A common progress billing schedule for a $50,000 kitchen remodel might look like:

1. Deposit: $12,500 (25%) due at contract signing
2. Progress payment 1: $12,500 (25%) due at completion of demo and rough-in
3. Progress payment 2: $12,500 (25%) due at completion of cabinets and countertops
4. Final payment: $12,500 (25%) due at final walkthrough and punch list completion

Include this billing schedule in your original estimate or contract so the client knows when to expect invoices. Then stick to it. Don’t let work get ahead of billing, or you’re financing the project with your own money.

Common Invoicing Mistakes That Cost You Money

Even with a good system in place, these mistakes trip up contractors regularly:

Waiting Too Long to Invoice

The number one cash flow killer. If you finish a phase on Tuesday but don’t send the invoice until the following Monday, you’ve already lost a week. Invoice the same day the work is complete. With Projul, you can create and send an invoice from the job site on your phone in under two minutes.

Not Following Up

Sending an invoice and hoping for the best isn’t a strategy. Set up a follow-up schedule:

• Day 1: Send the invoice
• Day 7: Friendly reminder if unpaid
• Day 14: Second reminder with a note about payment terms
• Day 30: Phone call and formal late notice

Projul tracks invoice status so you can see at a glance which invoices are paid, pending, or overdue.

Inconsistent Formatting

If every invoice looks different, clients question your professionalism. Use the same template every time. Same logo placement, same fonts, same line-item format. Consistency builds trust.

Not Tying Invoices to Estimates

If your invoice doesn’t match what the client approved in the estimate, expect pushback. When you create invoices from your approved estimates (one click in Projul), the numbers always match. No surprises for the client, no disputes for you.

Forgetting Change Orders

If you did additional work beyond the original scope, that work needs its own line item on the invoice, tied to a signed change order. Billing for work the client didn’t approve in writing is a recipe for non-payment and disputes.

Tracking Invoices and Cash Flow

Writing the invoice is only half the job. You also need to track what’s been paid, what’s outstanding, and what’s overdue. Projul’s invoicing features show the status of every invoice across all your active projects in one dashboard.

At any given time, you should be able to answer these questions:

• How much money is owed to you right now?
• Which invoices are past due, and by how many days?
• What’s your average time from invoice to payment?
• Are certain clients consistently slow payers?

This data doesn’t just help with cash flow. It helps you make better business decisions. If a client consistently pays 60 days late on a “Net 30” invoice, you know to require deposits and shorter payment terms on their next project. If a certain type of project always has billing disputes, you know to be more detailed in your estimates and invoices for that work.

Your time tracking data feeds directly into your invoices when you’re billing time and materials, so every hour is accounted for and backed up by real records.

Wrap Up

Writing an effective invoice isn’t complicated, but it does require consistency and attention to detail. Choose the right tool, include all the necessary information, calculate your costs accurately, and make it easy for clients to pay. Do those four things on every invoice, and you’ll spend less time chasing payments and more time running your business.

Projul makes invoicing fast, accurate, and professional. From estimate to invoice to payment, everything is connected in one platform. Check out Projul’s invoicing page to learn more.

Try a live demo and see how Projul simplifies this for your team.

DISCLAIMERWe make no warranty of accuracy, timeliness, and completeness of the information presented on this website. Posts are subject to change without notice and cannot be considered financial advice.