Apps? Noooooo. For these things, you need a human. 

You get a hold of a property manager local to that area . . . ask them what market rents are for a 3/2/2 or whatever in that area. 

Julie Trivers The best resource for home rentals is the MLS.

You need to know your local rental market.

Candice A. Donofrio gave you the right direction.....follow her guidance....

What Michael Setunsky said... but you need to be working with an agent who can provide the numbers.

Candice A. Donofrio nailed this one!

One key ingredient to building a profitable Investment portfolio is a full service Property Manager ! It is not a DIY  !!!

Get to know the rental market, look at plenty of them and learn what they are worth.

Zillow is also a good method, if you are looking for entertainment and an empty rental.

It's all about knowing local supply and demand and current market rates. No apps. 

I work with a number of investor buyers from all over the country but I don't do any property management.  That said, through experience, I have developed excellent relationships with several of our local property managers.

When we've narrowed it down to a couple properties, I'll send my first choice Property Manager a short list and ask him to provide rental values for me as well as a guess as to which of the possible properties is most likely to get the highest quality tenant.

Then I crunch the numbers based on acquisition, repairs, vacancy, etc.  I took a course that lasted several days to learn how to calculate the ROI over time.  If you're not confident, you may want to refer it out and look over the agent's shoulder to learn along the way.

I'm closing on one tomorrow where I represent both sides.  The seller's have only had the property for 21 months, with almost 3 months vacant.  Between the rental income, repairs and the sale of the property, they have made over 37% ROI in that time.

BTW, my advice was not to sell!  Fortunately I represent the buyer too, so I may get to sell this one for the 4th time in a few years.

Just curious, what area are you in?

What Candice A. Donofrio said.  There are also numerous online sources for this as well. But, that too will take a humanoid to do the research. We ain't got no apps to replace humans ... yet. 

   Talk to local property managers.   Or, talk to an appraiser. 

As others have commented, look at the rental comps just like you would look at sold comps when preparing your listing presentation.  I don't work with rentals at all and neither does my brokerage, so I have no idea on rents.  I look on the MLS for rental listings as well as our top property management sites and even Zillow and other sites that list rentals.  It's a good question for your buyer to ask, and just use the data that is already out there to give them a range of what current rents are doing.

Julie,

Candice A. Donofrio is right.  There is great value in communicating with humans in the know.  Most know more than the Apps world. A

Check with a local Realtor.

No app for this.. you would do it the same as you would price a home for sale. .... look for properties that have leased recently in the area similar to yours.

Here, there are enough rental properties in our MLS to come up with our own data. I typically just pull up all the most recent rented units in a specific area and figure it out myself.

Local stats.

Look up the rentals in that community...just like you look up comps for a sale.

Check what they are asking and what they are renting for.

Eve

It's called look in the MLS, zillow and craigslist to see what things are actually being offered at and what they rented at (in the MLS).  The zestimated rents are useless as they don't take seasonal factors, natural disasters or inventory levels into account.

Depends on area, as around here, most landlords advertise themselves and not with an agent. We don't have rentals listed on our local MLS in Lincoln, but I believe our Omaha MLS does, but not sure how many homes are listed on there.  Again, depends on area where you live.  Things are run differently all over the country.  Even between Lincoln and Omaha, it's two different beasts.  For Lincoln, which is in a housing shortage right now, rentals are in high demand.  New apartment complexes are being built over night it seems.  This is also coupled with Nebraska's low unemployment rate too.   So your local economics should be your first clue as to rental price.

For our area, one way to research rental price is on Craigslist.  Lots of landlords list on craigslist in our area.  You could also check Zillow, which may not be that accurate, or even fair to tennant, but consumers around here swear by Zillow and seem to think their zestimates are correct, so might as well use that to your advantage. lol... just kidding.

Anyways, I found another site a while back called rentometer.com.  Enter the address, sq footage and # beds and it brings up rental comps.  It's free for basic info, but they have a paid section that dives into more details.  Thier mapping is pretty good and it shows the address of the rental comp and price rented or advertised.  As long as you have the address, you can do research on that property's specs on the county assessor and compare it to your rental.

Remember, all real estate is LOCAL.

Just do a rental cma.

Find a really great property manager, pay them what they deserve, and don't leave this up to rank amateurs.

Julie Trivers the apps can't do what the personal analysis can do! Not yet that intelligent, I believe.

You just have to do the leg work...no short cuts

You need a real estate expert to guide you. Finding the right one can be the difference between making a big mistake and making a great investment.

Anywhere they advertise for your area is a comp source. Also, visit with prop mgmt firms and or renters themselves and conduct a poll...

Study the local market and sdjust accordingly. It is not an exact science, but experience will make you better.

Agree with all answers

Great answsers are here.

I do not do rentals, so have potential clients call my property manager.

My first suggestion would be to use an agent who invests in real estate - there's nothing like having skin in that game and understanding rental rates.

Different areas bring different rates and those different areas can be one block from one another. So, not only do you have to know the rates but, you have to know your local geography like the back of your hand!

Sounds hokey but, I work with a serious investor who is also an agent and I can consult with him about rental rates or anything tenancy and he'll get me down to the penny and know the fine print of lease agreements & tenancy law like no 'normal' buyers agent.

Seek someone who KNOWS what they are talking about - and it's not every buyers agent who claims to be able to do it all either!

Refer to your managing broker...

Best way is to do your own rental CMA for the area.