Patrick Rettig Architect LLC

Construction Budget Calculator

Residential Construction Budget Calculator

All residential construction projects should start with a discussion and consideration of budget goals. The earlier in the process the homeowner can establish a target budget, the more efficient the planning and design process will be, and the more likely it is that the built project will be in line with homeowner's vision. 

Of course, as any contractor will tell you, it's impossible to estimate the cost of a construction project before it's "designed", that is, before the extent, complexity, and specifics of the work are established. This is certainly true. But we still need to start somewhere, and the earlier the better, even if our initial rough budgets need to be revisited and revised along the way.

This budget calculator grew out of an effort to improve the initial budgets we develop for our addition and renovation projects. Over time, I started to accumulate and break down residential construction cost data taken from various sources (mostly from job cost records of projects I've worked on personally over the last 15 years).  Eventually, I used this data to develop a spreadsheet that calculates construction budget numbers based on a number of key variables that I thought could be established - or at least reasonably guessed at - very early in the process, based on the homeowner's stated goals.

This budget calculator has served me and my clients well over the years, and recently I decided that I would make it accessible to other construction professionals and homeowners in an effort to start a conversation about construction costs and the variables that drive those costs. Please submit a contact form (click on the Contact heading at the top of the page) with any comments, questions, or ideas for improving the calculator. 

This is a tool intended to be used for early-stage rough budgeting only. It develops budgets using rough project parameters and is intended to be used by homeowners, contractors and architects to help structure early stage decisions about whether and how to pursue a particular construction project for a single or two family house. In most cases, the best results will be achieved when a homeowner and qualified construction professional (an architect or general contractor who has experience with the specific project type in question) work together as a team to develop the input parameters.

Quick Tips

  • The calculated budget number accounts for construction "hard" costs only. You will need to include other project related "soft" costs to arrive at a total project cost (see detailed notes below).
  • Add a contingency to the budget number calculated by this application (10% - 30%, see detailed notes below).
  • Don't forget to include square footage for work that is incidental to the main project, but still required to fulfill the project goals. For example, the main project is a master suite addition, but you might also need to renovate a bedroom to create access to the addition and repurpose the space. (see detailed notes below).
  • Some square footage reference numbers:
    • A typical small bedroom might measure 12' x 12', approximately 150 sf
    • A master bedroom suite with full bath can range in size from approximately 250 sf (smaller) to 375 sf (mid range) to 500 sf and up.
    • A typical small dining room might measure 12' x 12', approximately 150 sf. A dining room in a larger home might occupy 250 - 300 sf.
    • A typical small 3 fixture bathroom with 36" vanity, toilet and tub on the same wall measures 5' x 8', approximately 40 SF
    • A typical small 1/2 bath occupies approximately 20 - 25 sf
    • Larger master bathrooms can occupy 100 - 150 sf and up.
    • Kitchens range widely in size, from small galley kitchens (100 sf and under) to large kitchens with multiple islands and eating areas (600 sf and up). A typical well equipped, functional kitchen in an average house ranges from 130 - 200 sf.
    • To help establish the square footage of your existing house (without pulling out a tape measure) you can search the assessor's database for your town (e.g. The record should include a line drawing of your home's footprint and square footages for the various floor plates of the various volumes. In my experience some of this information can occasionally be incorrect, so be sure to double check the critical areas. 


More Detailed Notes

  • The results are only as good as the inputs submitted and the general assumptions inherent in the formulas. The tool should only be used in the absence of other, more scope specific, budgeting options.
  • This Budget Calculator is set up using google forms, a google spreadsheet and an add on that can auto send the result of the calculations to an inputted email address. Unfortunately the application will not work without an email address, however this is my application running on my system accessible only by me, and I promise not to share any email addresses with third parties.
  • The budgets developed by this Budget Calculator are not estimates of construction costs. An estimate is developed by a qualified contractor based on detailed scope information, usually conveyed by means of architectural drawings and specifications.
  • It is important to incorporate all the square footage to be renovated into the "Major Renovation" or "Minor Renovation" numbers, even if some of the square footage is occupied by a bath or kitchen which is the subject of other questions. For example, if the project in question is a partial first floor renovation that includes a complete renovation of the kitchen, half bath and dining room, and just some painting and miscellaneous work at the living room an office, inputs might look like this:
    • Finished Area of Major Renovations: 350 (square footage of the kitchen, dining room and 1/2 bath)
    • Finished Area of Minor Renovations: 450 (square footage of the office and living room)
    • Kitchen: Renovate existing kitchen, keeping existing layout
    • Size of Kitchen: 175 (sf of kitchen)
    • Bathrooms - Remodeling: 2 (half bath with two fixtures - a pedestal sink and a toilet)
  • A major cost component of most addition projects will be the renovation work required to tie the new addition into the existing house and create a good, functional overall floor plan. For example: An addition to the rear of an existing house which will include a new kitchen will also require the renovation of the existing kitchen space, and possibly the existing dining room space. This work needs to be accounted for in the budget and the square footage should be added to the total in the Finished Area of Major Renovations field along with other areas to be renovated. It can be difficult to foresee all the areas and impacts that will need to be addressed as the design work proceeds, however there are almost always some impacts to the existing house and some estimate of these impacts should be incorporated into the budget. Experience with residential addition and renovation projects is helpful in predicting the potential scope of these impacts. 
  • Currently the application only includes location factors for Massachusetts cities and towns.
  • The construction cost data used to develop this calculator includes all typical construction hard costs, including allowances for fixtures and finishes related to the work of the project (e.g. plumbing fixtures, lighting fixtures, tile, appliances, etc.). Other project costs which you may need to budget for, but which are not incorporated in the the rough budgets generated by this application include:
    • Surveying, certified plot plan
    • Architectural design
    • Engineering (Structural, Civil, Geotechnical, etc.)
    • Interior design
    • Moving, storage, or temporary relocation costs
    • Utility costs
    • Any significant custom carpentry or built-ins
    • Furniture, window treatments, etc.
    • Landscaping
    • Contingency to account for:
      • Roughness of parameters and formulas used in developing early stage budget numbers
      • Uncertainty of scope at early stage of project development
      • Potential concealed and unforeseen conditions encountered during construction
      • Potential increase of labor and materials costs occurring from the time the initial budget is developed to the time that pricing is locked in.
      • Note, the adequate contingency percentage for a given project depends on a number of factors specific to that project, as well as the owner's risk tolerance. Recommended contingencies are generally in the range of 10% - 30% of construction cost at the early stage, and that number can be decreased during the course of the design process as the scope becomes better defined and more accurate estimates are developed. 
  • The application is currently not set up to account for certain work items that you may find to be a significant part of your project scope, for example the installation of a new air conditioning system serving the entire house when the base project is a master bedroom addition. In these cases, the best strategy is to focus on budgeting the base project using this application and then adding a budget for the work items additional to the base project on top of this number.