Contractor Job Costing, Retainage and Progress Billing Guide

A general contractor in Coral Gables can finish a $2.4 million build out under budget on materials and labor, hand over the keys, and still end up cash poor because the bookkeeping never tracked where the money actually went. Contractor job costing, retainage accounting, and progress billing are not optional add ons for construction businesses. They are the difference between knowing which jobs make money and guessing. If your books only show total revenue and total expenses for the year, you are flying a $500,000 project without instruments.

This guide breaks down how South Florida general contractors, subcontractors, and construction firms should structure their bookkeeping to get accurate job costing, manage retainage properly, and bill progress work in a way that keeps cash flowing instead of stalling behind schedules and change orders.

Why Contractor Job Costing Is Different From Standard Bookkeeping

Job costing means tracking every dollar of revenue and expense at the individual project level, not just at the company level. A standard profit and loss statement tells you the business made $180,000 last year. Job costing tells you that the Brickell condo renovation made $42,000, the Pinecrest addition lost $6,000, and the Coral Gables custom home is still $30,000 undecided because retainage has not been collected.

For general contractors, three cost categories need to be tracked separately on every job:

1. Direct labor, including payroll taxes and workers' compensation allocated to that specific project
2. Materials and subcontractor costs, tied to purchase orders and invoices for that job number
3. Equipment and overhead allocation, a reasonable percentage of insurance, vehicle costs, and office overhead assigned proportionally to each job

Without this breakdown, a contractor cannot answer the most basic question in the industry: which types of jobs, clients, or project sizes actually generate profit. A construction firm that bids the next job based on gut feeling instead of real historical job cost data is guessing at margins in a market where material prices and skilled labor availability change month to month across Miami-Dade County.

Setting Up a Job Costing System That Works

The most reliable approach uses a job costing structure inside your accounting software (QuickBooks Online, Sage 100 Contractor, or Buildertrend integrated with accounting) where every transaction, whether it is a payroll run, a lumber yard purchase, or a subcontractor invoice, gets coded to a specific job and cost code.

A basic cost code structure for a mid-sized general contractor typically includes:

• Site work and permits
• Foundation and structural
• Framing and labor
• Electrical, plumbing, HVAC subcontracts
• Finishes and materials
• Overhead allocation

When every transaction is coded this way, your firm can run a job profitability report at any point mid-project, not just after closeout, and catch cost overruns while there is still time to issue a change order.

Retainage Accounting: The Money You Have Earned But Cannot Touch Yet

Retainage (sometimes called retention) is the percentage, typically 5% to 10% in Florida construction contracts, that a client or general contractor withholds from each progress payment until the project reaches substantial completion or passes final inspection. This money is legally yours, but it is not cash you can spend, and it needs its own line on your balance sheet, not buried inside accounts receivable as if it were a normal invoice.

Here is where many contractors get their bookkeeping wrong: they record the full invoice amount as revenue and accounts receivable, then never separately track that 10% held back. Six months later, when the retainage finally releases, it shows up as a mystery deposit that nobody can tie back to the original job.

Example calculation: A South Florida contractor bills a client $180,000 for a completed phase of work, with a 10% retainage clause. The correct entry is:

• Accounts receivable (collectible now): $162,000
• Retainage receivable (held until completion): $18,000

That $18,000 does not disappear from your books, it moves to a separate retainage receivable account so your team can track exactly how much is owed across all active jobs. A contractor running four simultaneous projects each holding back 8% retainage on $250,000 in billed work per project has $80,000 sitting in retainage receivable that needs to be monitored and collected, not forgotten.

Retainage Payable to Subcontractors

The same logic applies in reverse. If you are the general contractor withholding retainage from your subcontractors, that amount is a liability (retainage payable) on your books, not an expense you have fully paid yet. Getting this wrong overstates your expenses in the current period and understates them when retainage actually releases, distorting job profitability reports and your tax picture for the year.

Progress Billing Bookkeeping: Getting Paid As You Go

Progress billing, also called schedule of values billing or AIA style billing, allows a contractor to invoice a client for a percentage of the total contract as work is completed, rather than waiting until the entire project is finished. This is standard practice on nearly every commercial project and most residential builds above a certain size in South Florida.

The core document is the schedule of values, a line item breakdown of the total contract price across each phase of work (site prep, foundation, framing, and so on). Each billing cycle, the contractor reports the percentage complete for each line item, and the client pays based on that percentage, minus retainage.

Example calculation: A $900,000 commercial build out in Miami has a schedule of values that allocates $150,000 to the electrical phase. At the end of month three, the electrician reports 60% completion. The progress billing for that line item is:

$150,000 x 60% = $90,000 billed to date

If $54,000 was billed in the prior period, this month's invoice for that line item is $36,000, minus the applicable retainage percentage.

Progress billing bookkeeping breaks down when contractors either bill inconsistently (guessing at percentage complete instead of using actual job cost data) or fail to reconcile billed to date against costs incurred to date. This mismatch creates two dangerous scenarios: overbilling, where you have been paid more than the work performed justifies, or underbilling, where you have completed work but not yet invoiced for it, effectively giving the client an interest free loan.

Over/Under Billing and Why It Matters for Cash Flow

Every month, a properly run construction bookkeeping system should generate a Work in Progress (WIP) schedule comparing:

• Contract value
• Costs incurred to date
• Percentage complete (based on cost, not guesswork)
• Amount billed to date
• Over billing or under billing position

A contractor who is underbilled $50,000 on one job is essentially financing that client's project out of pocket, which strains payroll and materials purchasing on other active jobs. Catching this monthly, rather than at year end, is one of the highest value functions of dedicated construction bookkeeping.

Why South Florida Contractors Face Unique Bookkeeping Pressure

Miami-Dade County's construction market moves fast, with material costs, hurricane season scheduling delays, and permit timelines all adding variability that generic bookkeeping cannot absorb. South Florida business owners in construction also deal with Florida's lien law timelines, which require precise documentation of billing and payment history if a Notice to Owner or lien claim ever becomes necessary.

Florida does not have a state income tax, which helps contractor margins compared to firms operating in high tax states, but it does not reduce the complexity of job costing, retainage tracking, or sales tax on materials, which Florida taxes at the point of purchase for most contractors under the improvement to real property rules. A Coral Gables based contractor bidding jobs across three counties needs bookkeeping precise enough to track sales tax paid on materials by job, not just in aggregate, to properly support cost basis and tax deductions at year end.

Step by Step: Building a Job Costing and Billing Workflow

1. Assign a job number to every project before the first dollar is spent, including bid preparation costs if material.
2. Set up a standardized cost code list used consistently across every job so historical comparisons are meaningful.
3. Code every transaction to job and cost code at the point of entry, not in a year end cleanup.
4. Reconcile the schedule of values monthly against actual costs incurred to determine true percentage complete.
5. Generate a WIP schedule every month, not just at tax time, to catch overbilling or underbilling early.
6. Track retainage receivable and payable in separate accounts, reconciled against each job's contract terms.
7. Review job profitability by phase, not just at completion, so change orders can be priced accurately going forward.

Contractors who outsource this workflow to a team offering managed accounting typically see cleaner monthly financials within one or two billing cycles because the coding discipline gets built into the process instead of reconstructed after the fact.

Tax Strategy Implications for Contractors

Job costing accuracy directly affects tax strategy. The percentage of completion method, often required for larger long term contracts under IRS rules, depends entirely on accurate cost tracking to determine taxable income for the year. A contractor with $3 million in annual gross receipts using the wrong revenue recognition method risks both an inaccurate tax bill and IRS scrutiny.

Provisions under the recent federal tax legislation, sometimes referred to as the Big Beautiful Bill, expanded bonus depreciation rules that matter significantly for contractors purchasing heavy equipment, vehicles, and tools. A contractor investing $200,000 in new equipment in 2026 needs job costing data to properly allocate that equipment's use across jobs, supporting both accurate job profitability numbers and defensible depreciation schedules if the IRS ever asks. Pairing solid job costing with proactive business tax strategy planning ensures that every dollar of legitimate deduction is captured without creating documentation gaps.

Common Bookkeeping Mistakes That Cost Contractors Money

• Recording retainage as regular revenue instead of a separate receivable, overstating available cash
• Failing to allocate overhead and equipment costs to individual jobs, making every project look artificially profitable
• Billing based on estimated percentage complete instead of actual costs incurred
• Mixing multiple jobs' expenses into one general "materials" account with no job tagging
• Waiting until year end to reconcile WIP schedules instead of reviewing monthly

Each of these mistakes compounds over time. A contractor running five jobs at once who miscodes even 10% of transactions can end the year with job profitability numbers that are off by tens of thousands of dollars, directly affecting bidding decisions on the next project.

Frequently Asked Questions

Q: What percentage of retainage is standard in Florida construction contracts? A: Most Florida general contractor and subcontractor agreements withhold 5% to 10% retainage, though this can vary by project size and whether the contract is public or private. Florida law caps retainage on certain public projects and requires it to be reduced as the project nears substantial completion, so contractors should review the specific contract language for each job.

Q: How often should a contractor run a job costing report? A: Ideally monthly, tied to the billing cycle, so that overbilling or underbilling positions can be caught and corrected before they compound. Waiting until project completion or year end to review job costs means losing the ability to adjust pricing or staffing mid project.

Q: What is the difference between progress billing and milestone billing? A: Progress billing invoices a percentage of each line item in the schedule of values based on work actually completed, while milestone billing ties payments to specific predefined events like foundation completion or drywall installation. Progress billing generally provides more consistent cash flow because it does not require waiting for a full milestone to be reached.

Q: Do South Florida contractors need to charge sales tax on labor and materials? A: In Florida, contractors generally pay sales tax on materials at the time of purchase rather than charging clients sales tax on the finished improvement, though the rules differ for certain contract types like real property improvement versus tangible personal property sales. Because this affects job costing and pricing, Miami-area contractors should confirm their specific tax treatment with an accountant familiar with Florida construction tax rules.

Q: Can small residential contractors in Coral Gables benefit from job costing, or is it only for large commercial builders? A: Job costing benefits contractors of every size because even a single $80,000 kitchen remodel has labor, materials, and overhead costs that need tracking to know if the job was actually profitable. Small residential contractors often see the biggest improvement in bidding accuracy once they start comparing historical job cost data across similar projects.

Q: What is the biggest bookkeeping mistake general contractors make with retainage? A: The most common mistake is recording the full invoice amount as collected revenue without separating out the retainage portion into its own receivable account. This overstates available cash and makes it harder to track exactly how much money is still owed across multiple active jobs.

Getting Your Contractor Bookkeeping Under Control

Job costing, retainage accounting, and progress billing are not back office paperwork, they are the financial control system that tells you whether your construction business is actually making money on the jobs you are bidding and building. South Florida general contractors operating in a fast moving, high cost market cannot afford to guess at job profitability or lose track of retainage owed across active projects.

WAYG works with general contractors and construction firms across Miami-Dade County from our Coral Gables headquarters, building job costing systems, WIP schedules, and progress billing workflows that hold up to scrutiny and give owners real time visibility into every project. Whether you need small business bookkeeping set up from scratch or a virtual CPA relationship to review job profitability and tax strategy together, our team understands the specific pressures facing contractors in South Florida's construction market.

Contact WAYG today to schedule a consultation and get a job costing and retainage system in place before your next bid goes out the door.