So far with the properties that have looked promising we have utilized the calculated NOI / Cap rate to determine the value and every one we have done has come up way lower than the asking price and in one instance came up less that what the current owner paid for the place initially.

Understanding where the market is can help you make better decisions.Use Helpful Tools:Real Estate Apps: Apps like Redfin and Realtor.com offer a lot of info on property values and market trends.Deal Analysis Tools: Consider tools Biggerpockets calculator, they offer a variety of calculators that are very easy to use! 

When rents and occupancy vary as seasons change, how do you average that out to enter it in the calculator?

Make sure to factor in possible rate hikes when calculating your future expenses.Regarding your offer and projected numbersOffer Price Offering $525K on a property listed at $619K is a significant reduction.

Is there an online calculator for this?

This is rent minus mortgage PITI and property management fee 10% (I don't include capital expenses in that calculation since I already set aside a reserve fund and the HVAC and water heater are 5 years old.

One thing thats hard to calculate is rent growth.

Upfront expenses and monthly payments must be considered when calculating the return on your investment.EXAMPLEI will provide details below, but here's the short version for those who hate to read or do math.

Search on this forum and you can see the buffer contingency numbers which people how have invested and got burnt come out with and maybe use  a median to calculate based on that:)

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