what do people think about this deal ?

[Dylan Badinghaus]

Hi everyone ! I am running numbers on a duplex and wanted to double check and make sure i have everything covered and see what people think. Asking price is $99000  rents are $600 per side and tenants pay all utilities  . Owner said has long term tenant on one side of 9 years , building has had  great rental history. 

600*2=1200 monthly

1200*12= 14400 yearly 

taxes/insurance =2800 yearly

repairs/maintenance 10%= 1440

vacancy 10%=1440 

14400-2800-1440-1440=8720 NOI

20% down on 99000 @ 4% interest 30 years =19980 

mortgage payment roughly 382 a month /382*12= 4584

(NOI )8720 - (debt service )4584= 4136 monthly cash flow

cash flow 4136 / (money invested) 19980 =20% ROI

Am i missing anything here ? Would you alot more than 10% for repairs and 10 % for vacancy ?