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Cost-plus, or time-and-materials bids are often used on jobs with a lot of unknowns and hidden conditions, such as repair work. While generally used for smaller jobs, these contracts are sometimes used for large jobs as well. Whenever the plans and specs are fuzzy for whatever reason (never a good idea), cost-plus may be the only way to proceed.

On jobs with many unknowns, the client can benefit from cost-plus pricing, in theory, because the contractor does not have to add big “fudge factors” into his fixed bid to cover the unknowns. The homeowner pays only for the actual work completed. Without adequate protections built into the bid, however, the owner is taking on an enormous risk that job costs will spiral out of control. There is little incentive for the contractor to get the job done quickly and cheaply.

In general, cost-plus work is an open book process where bills from the contractor include documentation of all hard costs. This would include invoices for materials and subcontractors, as well as work hours and billing rates for direct labor supplied by the contractor. This is a trust-but-verify process to ensure that the contractor is keeping good records and billing responsibly.

The two main variations of this approach to bidding are cost-plus-a-percentage and cost-plus-a-fixed-fee.

Cost-plus-a-percentage. In this scenario, the contractor bills the client for his direct costs for labor, materials, and subs, plus a percentage to cover his overhead and profit. The problem with this approach is that the contractor has no real incentive to complete the job quickly or cheaply – the longer he takes and more he spends, the larger his profit — not necessarily a good deal for the owner.

Cost-plus-a-fixed-fee. In this scenario, the contractor bills the client for direct costs, plus a fixed fee for  overhead and profit. In this case, the contractor is motivated to complete the job quickly and cheaply, or his overhead and profit percentage keeps dropping. If the customer increases the scope of work through change orders or a changed scope of work, then the customer and contractor would need to renegotiate the fixed fee or follow a prescribed formula.

Estimates. Nearly all cost-plus work comes with an estimate of costs. As with a  fixed-price bid, the estimate should contain detailed plans and scope of work, and material specifications, along with an itemized breakdown of costs. An exception would be an emergency repair, where there is no time for a detailed estimate, so a ballpark estimate will have to do.  However, it should be made clear that all cost-plus “estimates,” are a best guess, not a fixed bid. The greater the unknowns, the less precise the estimate will be.

Guaranteed maximum. When clients are concerned that job costs will spiral out of control, some contractors will provide a guaranteed maximum price.  In one version, the contractor will split the savings with the customer if the job comes in below the maximum. In this case the contractor has an added incentive to beat the maximum price (or the set the maximum price high enough that he can easily beat it).

A similar approach is to negotiate a flat fee with an incentive bonus if the job comes in on time and on budget. I’ve also seen cost-plus contracts where the owner has the right to terminate the contractor if the owner is over budget by a certain percentage at any draw by the contractor. The goal is to build in some protections and incentives to help protect the owner from a runaway budget.

Defining job costs. For this approach to work, it’s essential that the contractor make it clear to the owner which costs will be considered direct job costs – and therefore reimbursable. The obvious costs are subcontractors, materials and supplies used on the job, such as lumber and nails, along with consumables such as plastic sheeting, bits, and blades used up on the job. For labor, the reimbursable rate typically includes “labor burden” of employee taxes, benefits, and insurance.

Incidental costs like dumpster fees, permit fees, and equipment rental are typically included. Other costs are subject to negotiation: rental/usage fees for equipment owned by the contractor, vehicle expenses, insurance costs. As an owner, I would expect these to be covered by the contractor’s overhead, but either way, it should be clear what you will be billed for as a job cost.

A related issue is the contractor’s time spent on job supervision. Generally, this is reimbursable if he is on the job site overseeing subs or his own crew (or swinging a hammer himself). Management time off-site is generally not reimbursable unless specific tasks are listed as billable, such as making owner-requested plan revisions.

Pros of cost-plus-a-percentage

  • For jobs with a lot unknowns, contractor does not have to pad the price for uncertainty.
  • Can get started quickly on jobs with many unknowns and incomplete plans.
  • You pay only for work completed, with open books, at a known rate.

Cons of cost-plus-a-percentage

  • Contractor has little incentive to keep costs down.
  • Owner assumes all the risk of cost overruns
  • Requires high level of trust in contractor

Pros of Cost-plus-a-fixed-fee

  • Same advantages as Cost-plus-a-percentage”
  • Contractor has a greater incentive to complete job on time and on budget.

Cons of cost-plus-a-fixed-fee

  • Owner assumes most of the risk of cost overruns

Some people love cost-plus work, some hate it. In theory, it can save the owner money on jobs with a lot of unknowns, since the contractor does not have to pad his estimate to cover the unknown potential costs. In some cases, it probably does save money, but you will never know ahead of time – and you absorb most of the risk of cost overruns.

In some cases it is an easy fall-back for a contractor with limited experience in estimating. This is dangerous as neither you nor the contractor has much idea of what the project will end up costing.

However, with certain safeguards, cost-plus can work well for those jobs with a lot of unknowns. To protect yourself, I recommend the following:

  • Start with a detailed scope of work, with detailed plans and specs, so both parties have a clear understanding of the work to be down.
  • Use a cost-plus-a-fixed-fee contract, not a percentage.
  • Get a guaranteed maximum for peace of mind.
  • Get a clear list of reimbursable costs, to avoid misunderstandings.
  • Have the contractor provide detailed records of all reimbursable costs  when billing. This should be an open-book approach.

Related Links:  Are Supervision Costs Billable?     Cost-Plus for New Homes?   How Much Cost-Plus Markup?



  1. Huge Cost Overruns on Cost-Plus Remodel

    We are working with a contractor that we signed a time and materials contract with. We agreed to his estimate and had a reasonable amount set aside for overage. As of this week we have paid the agreed upon amount ($98,000). Based on his original estimate we still have $58,040 worth of work to be done. Some of his original estimates have tripled and quadrupled. What action if any do I have available. Please help!!!

    • buildingadvisor says:

      Sorry to hear about your situation. It’s a tough one, but unfortunately not uncommon with cost-plus contracts. I rarely recommend cost-plus contracts as the homeowner assumes all the risk of cost overruns and the contractor has little incentive to hold down costs.

      I wish I had better news for you, but the essence of a cost-plus or time-and-materials contract, is that you agree to pay the labor and materials necessary to complete the job. The estimate is typically non-binding. It is not a fixed bid, but simply an educated guess about what the project will cost. Since the word “estimate” is sometimes used to refer to a fixed-price bid, this is a frequent cause of confusion.

      Some cost-plus bids include a not-to-exceed (maximum) price or other cost controls, but most are open ended. Since invoicing is usually done on a regular basis, it should have been obvious to the contractor that the final cost was going to far exceed the estimate. At that point, the contractor should have discussed this with you as a matter of good business practice. However, he was not legally obligated to notify you that you were running over budget unless this was specifically stipulated in the contract – a good idea, but not common.

      Even if some of the cost increases were due to changes in the plans or specs after the work was started, you still should have been informed about the costs of any such changes.

      Time-and-materials contracts are typically open book. The contractor is supposed to provide the owner with detailed records of all costs, including actual invoices for materials and subcontractors if requested by the owner. Given the size of the overage, you are certainly justified in asking for full documentation of all costs before paying any additional invoices.

      You are also free to terminate with the current contractor and to find someone else to complete the work, if you think you can get the work done for less money. You can also try to negotiate with the current contractor to complete the remainder of the job for a fixed price, so you don’t get any further cost surprises.

      If you feel that the contractor intentionally mislead you, you may want to file a complaint with your state’s contractor licensing board or consumer protection agency. It may also be worth consulting a lawyer, who may have other ideas, but I would be surprised. Best of luck with a tough situation.

      Read more about Estimating Errors & Cost Overruns

      • Thank you so much. Our house is torn apart and we need to come up with a solution to put it back together. This contractor has done work for other people we know and all we knew was that he is expensive. We have several line items on the original estimate that we will not be able to complete. What I have a hard time understanding is certain things like brick work, soffit, fascia and gutter prices tripled. He knew the size of the addition so why would these numbers jump up so much?

        Is there any recourse if we feel that he low bid to get the job?

        Thank you so much for your time in this. Hopefully we will be able to find a solution.

        • buildingadvisor says:

          Did you make a lot of changes to the plan after the contractor provided an estimate? Assuming that you did not make huge changes to the plans, it’s hard to say why the estimate was so far off. Either they did a very poor job with the estimate or, as you suggest, may have intentionally submitted an unrealistically low bid to get the job.

          Did you get other estimates for this work and were they in line with this contractor’s original estimate?

          If you feel that the contractor has acted dishonestly you can file a complaint with your state’s contractor licensing board or state consumer protection agency – often part of the attorney general’s office. In some states, these agencies can help you file a complaint and help you resolve the dispute through mediation or arbitration. Many of the jobs that end up in arbitration are based on cost-plus contracts according to a construction arbitrator I know.

          In preparation for any form of dispute resolution, you should start documenting everything you can about the job. Take photos of the work completed, keep copies of all written correspondence, and keep a dated log of all conversations with the contract. Good documentation is critical to presenting your case in any type of proceeding.

          You can also contact a lawyer to see whether there is any other legal recourse. Low-bidding to win a contract can constitute fraud on public works projects, but I’m not sure if the same holds true for a residential cost-plus contract.

          Again, best of luck with finding a solution.

          • Thanks again. We made no changes to the original plan. We did purchase upgraded sliding doors and that was the only thing we did that may have been different from the original bid. We were aware of the price increase for said doors. We can account for about $5000 for the upgrade.

  2. Questionable Charges on Cost-Plus Job

    In the midst of reconciling a cost plus percentage contract. The owner provided four additional allowances to be built into the design build contract to cover change order related costs. The GC used an affiliate (family member) company, non-disclosed, to perform general site maintenance tasks. The contractor and the affiliate company were based two hours away from project. It would appear that a number of costs that should have been applied to the base contract were rolled over into the various allowances. In addition, the labor portions of the affiliate were lump summed together, so it is nearly impossible to allocate costs and many of the tasks that were invoiced were not remotely within the scope of the allowance.

    I found where we had been invoiced for a $2300 laser level had been purchased and was told that it was common practice that we allow the GC to keep the equipment as it would be cheaper than renting it for the three weeks it appeared to be in use. I’m getting push back when asking for a cost breakdown for a $13k punchlist that had been allocated to a fire sprinkler allowance.

    None of the tasks on this list were remotely associated to the the scope provided in the allowance. Why are we paying X amount to have debris cleared from a roof? Isn’t it the GC’s responsibility to backcharge the contractor that failed to clean up after themselves? I thought that this was a transparent process, but not so sure anymore.

    • buildingadvisor says:

      In most cases, I do not recommend cost-plus contracts for large jobs as they often lead to cost-overruns and disputes with contractors. It’s always difficult, at a distance, to untangle these sorts of issues. For example, I’m not sure what you mean by “the owner provided four additional allowance items”.

      In general, cost-plus contracts do not make use of allowances and change orders as work is billed on a time-and-materials basis. So it’s not clear to me why some of the work was billed by cost-plus while some has been “rolled over” into allowances. Perhaps you have a hybrid contract of some sort. There are an endless number of possible variations and I don’t know the particulars of your contract.

      However, it sounds like the contractor has not done a good job of communication and transparency in billing, which should be an underlying principle of any cost-plus contract. Some contractors are very good about this, while others need to be asked to see detailed invoices of materials delivered and work completed. Some contractors are disorganized and cannot easily provide good records – in which case you can never be confident that you are being billed fairly. There needs to be a certain level of trust for this to work as you cannot be on the job every day counting who worked for how many hours.

      Being invoiced for a $2300 laser level is definitely not appropriate. While tool rentals and “consumables” such as drill bits and blades are often included in billing, the purchase of a laser level is way out of line. Sounds like they bought a very high-end unit at your expense. In general, a laser level is a basic tool that the contractor would be expected to own. And even if they needed to rent special equipment for your job, the rate should be well below the price quoted – I would guess $100 to $200 per week at most.

      Sounds like you need to schedule a meeting with the contractor to go over the billing procedures and invoices. Don’t be afraid to ask for explanations if anything is unclear. You may want to have a friend or advocate sitting in with you if you think that would be helpful. If the contractor cannot provide a clear record of billable job costs, then you will need to decide whether you wish to contest the charges. At that point, it would probably be a good idea to speak with a lawyer.

  3. Lynn jaynes says:

    Should We Pay Markup on Tax?

    I do not think a fee should be charged on the tax…in other words, on a cost plus 25% basis, 25% of the cost of any labor and any product would be charged to the client, PRIOR to tax being added to total charge. Is this correct?

    • buildingadvisor says:

      There are no hard-and-fast rules about this or any other building contract – each contractor has his own recipe for coming up with a price. Cost-plus work seems pretty cut and dried, but it is not always 100% clear what is a direct cost that should be marked up and what should be counted as overhead, especially supervision time by the owner.

      For example, see this link on Billing For Supervision.

      The general concept, however, is that the contractor is marking up all direct costs attributable to a specific job. That typically would include sales tax he has to pay on materials. It would also include “labor burden,” that is, his true cost of hiring a worker, not just his hourly rate. That might include payroll taxes, worker’s comp, and other employee benefits. So some of his taxes are typically included in direct costs and marked up as you describe.

      Cost-plus bids should be “open book.” You should be able to see where to money is going and what is being charged as a direct cost. It is best to discuss these issues clearly at the outset to avoid misunderstandings half way through the job.

      You can read more on the at Cost-Plus FAQs.

  4. Can Labor Costs Exceed Cost-Plus Estimate?

    If you go with a cost-plus-a-percentage contract, can even the labor costs go higher than what is in the contract?

    • buildingadvisor says:

      Sorry to say, but with any cost-plus contract, the labor costs can definitely go higher than the estimate. In fact, the labor costs are the biggest unknown. On most jobs, it is pretty straightforward to price out the materials. It’s the labor that is most contractors have difficulty estimating.

      On a cost-plus job, the “estimate” is really just a best guess. On a fixed-price contract, people often use the terms “estimate” and “bid” interchangeably, causing some confusion. The bid price is a fixed price that is agreed upon to complete the described work.

      It is possible to put some limits on the price of a cost-plus job in the form of a not-to-exceed number if the contractor will agree to that. However, most contractors who work cost-plus resist putting any cap on the price.

      In general, I would avoid cost-plus on a large job, whether a new house or a large remodel. It’s just too risky for the owner, who holds all the risk for costs spiraling out of control. On a cost-plus-a-percentage, the contractor has little incentive to hold down costs. Cost-plus-a-fixed-fee is less common, but better for the owner as the contractor doesn’t profit from running over budget.



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