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Yet Another Cost Calculator

Discussion in 'Model 3: Ordering, Production, Delivery' started by mwu, Mar 27, 2018.

  1. mwu

    mwu Member

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    I made my own cost calculator based heavily on one I found somewhere (I can't remember where -- if you recognize it, please tell me so I can give credit). The justification for yet another calculator was to review monthly expenses the car would bring to convince myself and my wife that we could afford the car with a nice safety margin.

    Most calculators seem to follow cost of ownership which is great for looking at the value of a depreciating asset, but not so good at determining monthly costs and how that compares with another car. Instead of justifying the total cost of the car over the period of ownership, we wanted to understand how the car fits into our budget.

    This spreadsheet was instrumental in deciding that we could (I will be completing configuration and putting the $2500 non-refundable deposit down in a few days after shifting money around).

    The spreadsheet will need to be copied and customized to you and your area since it accounts for things like interest, tax, insurance, and energy rates. Mostly this just involves changing numbers, but you may need to change the formula for taxes which is specific to NC.

    Yet Another Model 3 Cost Calculator

    That said, Teslanomics calculator is pretty good -- I found it after I had built this. It provides a bit less detailed view, but does offer similar information.

    I estimate yearly costs up to five years with totals as well as yearly totals divided down to monthly values. In addition, you can put in equivalent values for an ICE vehicle to compare against and see yearly and monthly savings compared to that vehicle. I need a new car this year regardless of whether I got the Model 3, so I plugged in values from Edmunds for the a 2018 VW GTI Golf which is the car I might have purchased if we hadn't decided on the Model 3.

    We found that costs are pretty much upfront and savings are seen starting the second year. From there the savings increase rather dramatically. Affording the Model 3 for us was about ensuring we could comfortably get over that initial year hump and help fund year 2 with the tax credit.
     
  2. AviP

    AviP Member

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    Good job!
     
  3. insaneoctane

    insaneoctane Active Member

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    Nice work. I would suggest that your 4.4mi/kWh is too optimistic, especially if considering the charging losses.
     
  4. mwu

    mwu Member

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    Good point -- I think the original spreadsheet used that number and I just kept it. I assume the 310 mile range might not be an every day number (requiring slower driving). Assuming a 290 mile range would put the number at 3.87mi/kwh. Does that sound more reasonable?
     
  5. DurandalAI

    DurandalAI Member

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    If you think it might be a stretch financially or if your credit is not stellar, I would also recommend being pre-approved for a loan of the purchase price before you put down your non-refundable deposit.
     
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  6. mwu

    mwu Member

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    That's the funny thing, it isn't a big stretch and our credit is pretty darn good. It's just more than we have spent on a car before, and my wife was very nervous about that. Putting numbers in front of her and reviewing our budget put her at ease with adding the monthly cost.

    The car is replacing a VW Jetta that I purchased new 15 years ago when I had gotten my first job out of college. When I do the math, that was a higher percentage of my income than this will be... then again I have more expenses than I did then.

    On a side note, I should have sold the Jetta about 5 years ago. The first 10 years of keeping that car in shape was no sweat. The last 5 has seen it start to fall apart. The paint's clear coat is peeling and the interior plastics are degrading. Kinda sad -- I love that car.
     
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  7. BlueWRXPride

    BlueWRXPride Member

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    How did you determine your depreciation values for each car?
     
  8. mwu

    mwu Member

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    This is actually one area where I didn't try to be very accurate for the Tesla because it's a lot of guesswork right now. For the GTI, it's an educated guess based on depreciation of previous years of the GTI and maturity of the engine design and whatnot by Edmunds (where I got the depreciation values). I used the same percentages of loss of value for the Tesla.

    The Tesla may end up keeping value better than the GTI, but it's hard to say. Edmunds doesn't provide these values for the Tesla probably because they don't have previous models of Model 3s to compare against, the motor is different from previous Tesla vehicles, and even with previous vehicles there still isn't a lot of history on depreciation for Tesla vehicles or electric vehicles in general (at least not in the same way we have that same data for ICE vehicles) to generate models from and test those models against.

    I figure the spreadsheet gives me base values to estimate budget from. I just have to understand that the actual costs are going to vary. If the Tesla keeps value better than the GTI, then I'll pay higher property taxes, but get more out of it when I sell. If that's reversed, then I'll enjoy lower taxes, but I'll also have to weigh reduced resale value against not having a car payment.
     
  9. insaneoctane

    insaneoctane Active Member

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    I'd suggest using 3.5. Don't forget that you must consider charging efficiency here. Some people are reporting getting around 240 W/mi. If you use (1/3.5)=0.286 which ought to have enough margin for charging losses IMO.
     
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  10. insaneoctane

    insaneoctane Active Member

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    You may want to use this formula for depreciation....
    V = Vorig * e^- 0.18645*t

    Where
    Vorig is the original price
    t is year

    It assumes 18.6% loss per year
    Source of equation is here
     
    • Informative x 1
  11. mwu

    mwu Member

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    Ok, I see your point -- I was calculating based on the miles per charge without counting charging losses. Assuming about 20% losses from the wall to the battery comes to a very similar number to what your math comes to. Instead of combining the charging efficiency with the car's driving efficiency, I added that extra calculation to the top of the spreadsheet. Thanks for pointing that out.

    Hmm, ok. I do like having a formula to base it on rather than copying magic numbers from a web site.
     
  12. insaneoctane

    insaneoctane Active Member

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    Yes, and just like your desire to have the efficiency as an input above, you could have the 18.6% loss per year as an input to tweak as well....
     
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