Form 606 - expenses -
Form 607 - invoices -
Uploaded as "text file" (output from the same spreadsheet)
ITBIS, done once per month, via online form IT-1.
Income tax, once per year, IR-2.
A bit complicated in the beginning, but if you know accounting basics, doable on your own. Some exhibits won't apply to you, some I was straightforwardly suggested by a DR CPA to just "leave blank", that "for a small company nobody cares about them".
I do my own taxes for my two companies.
The biggest hassle is filling out 606 spreadsheet. The more receipts you get (invoices) from others, the more lines you have to fill out.
Also, I have had my own dose of "rectificacion" (corrections) dating back 18 months, and redoing all ITBIS declarations (all because of one incorrectly reported invoice in the beginning, when I was just learning the ropes).
Also beware that DR accounting is on ACCRUAL BASIS only, NO CASH BASIS. Your payment of ITBIS from your-issued invoices is due on the 20th of the next month REGARDLESS if you got the money from the client or not. Many decide not to pay and run the penalties and pay after they get paid from their clients.
The penalty is 12.58% for the first month and 6.58% for each additional month. This includes the penalty and 2.58% interest.
I found a way to "save" if you decide to run a penalty (e.g. the client didn't pay you and you have no money to pay ITBIS on time) - DO NOT report that invoice in that month (on IT-1). Rather, submit IT-1 without that invoice and once you get paid, do a RECTIFICACION (correction). You will only be liable for a penalty of 7.58% the first month and 4.58% each additional month *. A bit of work (you have to bring corrected IT-1 to the DGII, cannot be done online) but you can save some %% off.
* It's 50% of penalty (5% out of 10% and 2% out of 4%) plus 2.58% interest. You have to pay the lump sum of balance owed that was generated by that rectificacion to qualify.
Also, you should start building an ITBIS cushion. After you incorporate and get RNC#, you can start "collecting" your expenses and accruing ITBIS in your favor as a credit. This credit does not expire (no cash back either as they give you in Europe though). In a month when you owe a balance of ITBIS to DGII, from that balance will be deducted the balance of ITBIS you get in your favor that month, plus any balance you have in your favor from previous months.
Also, the penalty is only from the "net balance" of ITBIS you owe to DGII, not from the whole balance you generated that month.
P.S. I have RNC, NCF and ITBIS manuals form DGII. If your PM me your email, I can send them to you.