The latter describes your salary: if you sit at your desk and don't get fired, you'll get $500.
The former is more a description of the situation: somehow, by hook or by crook, I manage to scrape together $500.
The use of "per" imply a causal connection between the passage of time and the arrival of your pay.
"Each" encompasses the possibility there's no connection, and it's just happenstance.
english.stackexchange.com/users/4040/Malvolio
The two are equivalent.
Neither holds any implications as to how you come by the money; that is implied by 'earn'.
Per means 'for every' or 'for each', so it's almost exactly the same as just saying 'each'.
Per is perhaps more common.
english.stackexchange.com/users/None/
"Each month" is a fixed amount, "per month" can be an average.
english.stackexchange.com/users/4471/baquiano
I'd say that "I earn $500 per month" suggests that your monthly salary from a single source is $500, whereas "I earn $500 each month" could mean that you make $500 from potentially multiple sources.
english.stackexchange.com/users/4456/Junibert
"$500 per month" connotes "I earn money at a rate of $500 per month."
So if you work for half a month, you will earn $250.
"I earn $500 each month" implies that from the start of the month to the end of the month you acquire $500.
english.stackexchange.com/users/4460/Jake
There are subtle differences in meaning.
“I earn $500 each month” says that each month, considered separately, the sum of your receipts is $500.
This can mean that the sum equals $500 exactly .
But it can also mean $500 at least .
For example, you can write: I earn $500 each month.
During peak months, I earn as much as $800.
"I earn $500 per month” express a rate , or linear relationship, between time and money.
It means that over n months, the sum of your receipts is n × $500.
Again, this can mean that the monthly sum equals $500 exactly .
But it can also mean $500 on average .
For example, you can write: I earn $500 per month.
This is considering the year as a whole.
The summer months are slower, but I always make it up over the holidays.
english.stackexchange.com/users/14073/MetaEd
There is no difference.
The following sentences are equivalent: I earn $500 each month.
I earn $500 per month.
I earn $500 every month.
I earn $500 a month.
My [monthly] salary is $500.
From personal experience, I would say that per month is the least likely to be used in this context.
english.stackexchange.com/users/2705/Jimi Oke
What is the difference between these two sentences?   I earn $500  each  month   I earn $500  per  month
What is the difference between “I earn $500 each month” and “I earn $500 per month”?
english.stackexchange.com
<word-choice><prepositions><differences><syntax>
english.stackexchange.com/questions/10918
english.stackexchange.com/users/869/metal-gear-solid
It's possible that some people may perceive that the phrase "I earn $500 per month" describes your salary, whereas "I earn $500 each month" describes your situation. On the other hand, some people will say that these sentences are equivalent, although "per" is perhaps more common. In any case, the differences in meaning are subtle. There are differences in that the first sentence describes your fixed salary, wheras the second broadly describes your situation and denotes the passage of time before you are paid. However, some people do not see a difference in the two sentence as neither indicates how you earn the money. However, for some people "each month" is a fixed amount whereas "per month" can be an average. "per month" could be interpreted to mean a single source of income, whereas"each month" several sources of income. $500 per month" connotes "I earn money at a rate of $500 per month" whereas “I earn $500  each  month” says that each month, considered separately is the sum of your receipts is $500. There are subtle differences. It is suggested that "per" is the more commonly used form ,whereas some disagree with this.
It's possible that some people may perceive that the phrase "I earn $500 per month" describes your salary, whereas "I earn $500 each month" describes your situation. On the other hand, some people will say that these sentences are equivalent, although "per" is perhaps more common. In any case, the differences in meaning are subtle. There is some disagreement on the differences in practice, but 'per' and 'each' are near synonyms and can be used interchangeably here.
Per means 'for every' or 'for each', so it's almost exactly the same as just saying 'each'. However there are subtle diiferences, "Each month" is a fixed amount, "per month" can be an average.    The answer to this question is subjective. Some people believe that the two phrases are equivalent whereas others believe there are subtle differences. For example, "per" might imply an average whereas "each" may imply a fixed amount.
Describing 2 different things. There are similarities The differences Implying multiple sources of income Different meaning. Multiple sources of incoime
There is some disagreement on the differences in practice, but 'per' and 'each' are near synonyms and can be used interchangeably here.
More many people, the two phrases are entirely equivalent. For some people, "per" implies an average, whereas "each" implies a fixed amount.