Combined we are making about 250-300k annually pre-tax.

If we want to look at return on capital, the rate is much lower, because at the end of 4 years we'll have an asset worth ~$35,000 (if sold in a package to an investor) returning ~$4300 annually, but that is still a 12% return on capital.

In order to build wealth and make money work hard for me,I am thinking about how to use the equity I build.After I purchase the property,if the refinance LTV ratio is 70%,the value of property should increase about 40% to refinance all the capital invested in the property.And if the property appreciation compound annual 10%,it need take more than 3 years to get 40% increase.If the property does not appreciate a lot,the refinance does not worth it at all.So I need to use the capital I invested in the property more than once,I need to choose the property which has al lot of property appreciation.Anything wrong about my math?

.$180K CASH, $1,100 positive cashflow after HOA is only bringing in about 7% annually.

. $804.03 PITI $41.67 Sewer bill $146.50 Property Management (self) $146.50 Cap Ex $73.25 Vacancy Rate+$58.60 Utility/Misc$1,270.55- NOI-$1,465- monthly rent$194.45 Net Profit Income per month x 12 months = $2,333.40 Annual Net Profit IncomeTotal Deal Appreciation: $14,000- (38.25%) ARV was $101,000 Depreciation: $2,345.45- (6.3%) Amortization: $984.58- (2.68%) 1st year loan pay down Cash Flow: $2,333.40- (6.64%)*Property Management: $1,758- (5%) I self managehad script issues with bp website, could not rotate pics.     

Because adding in a modest 5% buffer for vacancy, the 10% for your property management, and maybe only 8% for maintenance.5% Vacancy: $1800 annually    /   -$150 monthly       10%  PM: $3600 annually         /   -$300 monthly8% Maint.: $2880 annually        /  -$240 monthlyMortgage, taxes, and ins

In this position, I think the best course of action is to seek out tenants that can sign annual leases.  

What I am confused about is that when I purchased the property, all 7 units were receiving $500 p/month for a gross monthly of $3500 and $42,000 annually.

If you are planning on just loaning the money for a very short time and that Annual rate is around 200% you should probably really dig into the laws around that.

If the unit has these:Assume replacement every 10 years:Water heater - $900Refrigerator - $900Range - $900Dishwasher - $600Clothes washer/dryer - $1000 combinedEvery 15 years:Furnace - $2900Central air - $29003 BR SFR Flat Roof - $2100 + $300 per 3 years to coat itI annually plan for an additional $1,500 of miscellaneous maintenance expenses and $800 for capital improvements.You could probably use something like this to estimate your per-unit costs as some units might not have all the same features.