Calculate paydays since a bill was last paid

I want a cell that calculates how many paydays have occurred since a bill was last paid. I have monthly, bimonthly, semiannual, and annual bills (I actually also have a semimonthly bill, but I just made it into two monthly bills). I keep trying different things, but it always gets something wrong.

Here’s what I have so far; it almost works, but I feel it’s also overly complicated and perhaps needs reworked from scratch.

IF(MOD(IF(DAY(TODAY())<Payday::$A$1,MONTH(TODAY())−1,MONTH(TODAY()))−(Start Month Rent+IF(Due Date Rent<Payday::$A$1,−1,0)),LOOKUP(Frequency Rent,Interval Values::$1:$1,$Interval))=0,IF(AND(DAY(TODAY())≥Payday::$A$1,DAY(TODAY())<Due Date Rent),LOOKUP(Frequency Rent,Interval Values::$1:$1,$Interval),0),MOD(IF(DAY(TODAY())<Payday::$A$1,MONTH(TODAY())−1,MONTH(TODAY()))−(Start Month Rent+IF(Due Date Rent<Payday::$A$1,−1,0)),LOOKUP(Frequency Rent,Interval Values::$1:$1,$Interval)))

“Start month” is the first month that the bill is paid during a year, for non-monthly bills.

The lookup table tells the formula what the bill interval is in months, so for “semiannual” it returns “6”.

Bills are always paid on the due date.

Paydays are monthly (on the 6th).

Help please? I’m having trouble wrapping my head around this.

(I’m on macOS Monterey, so I can’t use e.g. LET)