What would a fair share price would be to let my brother (also roommate) drive my car?

A lot of factors to consider. Insurance, wear & tear and so forth.

The IRS has a rate that it deems reasonable. 54.5 cents a mile.

That might be a bit high depending on various factors.

If he is buying his own gas, you wouldn't charge that much.

Id say some middle ground that both sides can agree on might be fair. But, he already tore up one car.

If he tears up yours and was only paying you 12 cents a mile, you aren't going to be happy.

Id say something in the 30-40 cents a mile range would be fair. If he buys his own gas. If you buy all the gas, you'd want more.

Can he be added to your insurance for free ? If not, more for that.

IR-2017-204, Dec. 14, 2017

WASHINGTON ― The Internal Revenue Service today issued the 2018 optional standard mileage rates used to calculate the deductible costs of operating an automobile for business, charitable, medical or moving purposes.

Beginning on Jan. 1, 2018, the standard mileage rates for the use of a car (also vans, pickups or panel trucks) will be:

54.5 cents for every mile of business travel driven, up 1 cent from the rate for 2017.

18 cents per mile driven for medical or moving purposes, up 1 cent from the rate for 2017.

14 cents per mile driven in service of charitable organizations.

The business mileage rate and the medical and moving expense rates each increased 1 cent per mile from the rates for 2017. The charitable rate is set by statute and remains unchanged.

The standard mileage rate for business is based on an annual study of the fixed and variable costs of operating an automobile. The rate for medical and moving purposes is based on the variable costs.

Taxpayers always have the option of calculating the actual costs of using their vehicle rather than using the standard mileage rates.

A taxpayer may not use the business standard mileage rate for a vehicle after using any depreciation method under the Modified Accelerated Cost Recovery System (MACRS) or after claiming a Section 179 deduction for that vehicle. In addition, the business standard mileage rate cannot be used for more than four vehicles used simultaneously. These and other requirements are described in Rev. Proc. 2010-51.

Notice 2018-03, posted today on IRS.gov, contains the standard mileage rates, the amount a taxpayer must use in calculating reductions to basis for depreciation taken under the business standard mileage rate, and the maximum standard automobile cost that a taxpayer may use in computing the allowance under a fixed and variable rate plan.

It depends how long.

If your brothers car died and he didn’t know it was going to die or DID know, yet still didn’t implement a plan to immediately replace it when the time came considering it sounds like he still NEEDS a car, I wouldn’t let him drive it. When your car eventually dies, he’ll be just as helpful replacing your car as he was his own.

I never liked sharing cars. Tell him to get his own.

You don't charge your brother. You share gas and maintenance.

Sell the car to your brother for the actual market value of the car. Use KBB.com to determine cash value.

At minimum, he should pay the difference in insurance (he needs to be a named driver) if not share it 50/50. And there is wear and tear that will occur (tire wear, for example), so I'd also charge him something in the neighborhood of the standard government tax-deduction rate on vehicles used for business owners. That's somewhere between 17 cents a mile and 54 cents a mile, depending on the vehicle and the usage.

If you’re going to do this then first work out what proportion of the total annual car mileage his 2k per year will be and then the total running costs including maintenance.

So if the car does 10k miles per year his share will be one-fifth.

But you then need to account for the annual resale price depreciation of the car. Work that out and if the car is fairly new that can be thousands of dollars per year, and if I was in your shoes I’d charge him half of that figure as if he had his own car he’d be paying 100% of that even if the car stayed parked the whole year.

You might see that differently and decide to charge less and that’s up to you. But think of what he’d have to pay for taxis and public transport every year if he wasn’t using your ride.

It’s admirable that you don’t wish to overcharge him, but it’s also vital not to short change yourself.

How much would uber charge? that would be a fair price to pay.

Don't do it. You will have disputes when you both want to use the car. What will happen when he writes it off?