Is it true that Uber and OLA drivers are making nearly a Lakh rupees per month in India?

As far as I know there is no fixed salaries given to drivers either in Ola Cabs (company) or Uber (company) they are paid for rides which means drivers get income only if they ride.
In initial days both this cab companies used to pay more incentives in additional to ride amount thus they used to get more money similar to the figures said by you and also each cab driver will be registered in the different cab operators such that making themselves always busy, but fuel expenses and vehicle maintenance should be done by drivers only.
Now the amounts they are getting has been decreased, many reasons for this, firstly cab operators reduced the incentives and increase of cabs also a factor. But still they are getting good amount.

An Expected Calculation of their Previous Income :-

I am a frequent user of Ola and Uber. It is fair to assume that these drivers make nearly a lakh rupees per month. I am also assuming that these drivers are the owners driving the cars. As said by others, it depends on the number of hours you put it, the distances of your trips and the timing of your trip. Here is how it matters.
1. Number of Hours  - Simple logic. The more is the number of hours you put, the more you earn. I have met some drivers who put in 14-15 hours daily. Most of the drivers work on this principle.
2. Distance of the trips - Both Ola and Uber keep on running the promotions for drivers also similar to customers. e.g Do 10/12 trips during the day and get 1600/2000 rupees at the end of the day. So here it depends on only the number of trips you do. If you are lucky to get most of trips for shorter distances your diesel consumption is lower and you benefit from it more.
3. Timing of the trip - If a diver is consistently operating between peak hours of the day his earnings are more. In addition to that, these companies keep running promotions. e.g. Do 10 trips during peak hours and 2500 rupees as flat income. Although it is not everyday promotion it does help these guys earn more. Plus you can make more trips during Non-Peak hours and increase your earnings.

Uber drivers used to earn ~ 1 lakh back when it started it's operations in india. At that time Uber didn't deduct any commission from ride, plus the drivers used to get lots of incentives. Now uber has started taking a percent of commission from the ride amount and the rest goes to driver. I've talked to many Uber drivers who seem quite frustrated as Uber has stopped giving them incentives too. Currently an Uber driver roughly makes ~15-18k per week. If you deduct the fuel charges and car maintenance, their net income won't be more than 40-50k per month

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