Calculate Payback Period

[G]

I am trying to figure out how to count the number of days it takes to get
paid back the investment that was paid 50% upfront and 50% midway through the
term of the deal.

I want to be able to automatically fill in the range within the countif
formula with a link to a cell that contains the calculated cell point.

Startpoint = E1
Midpoint = E30
Endpoint = E60
Midpointvalue = 30

Formula:
=if(countif(midpoint:endpoint, "<0")>0,
countif(midpoint:endpoint, "<0") + midpointvalue,
countif(startpoint:endpoint, "<0"))

Intrepretation:
=If(countif(E30:E60, "<0")>0,
countif(E30:E60, "<0") + 30,
countif(E1:E60, "<0"))

The values in the Range:

$(3,625.00)
$(3,425.00)
$(3,225.00)
$(3,025.00)
$(2,825.00)
$(2,625.00)
$(2,425.00)
$(2,225.00)
$(2,025.00)
$(1,825.00)
$(1,625.00)
$(1,425.00)
$(1,225.00)
$(1,025.00)
$(825.00)
$(625.00)
$(425.00)
$(225.00)
$(25.00)
$175.00
$375.00
$575.00
$775.00
$975.00
$1,175.00
$1,375.00
$1,575.00
$1,775.00
$1,975.00
$(1,450.00)
$(1,250.00)
$(1,050.00)
$(850.00)
$(650.00)
$(450.00)
$(250.00)
$(50.00)
$150.00
$350.00
$550.00
$750.00
$950.00
$1,150.00
$1,350.00
$1,550.00
$1,750.00
$1,950.00
$2,150.00
$2,350.00
$2,550.00
$2,750.00
$2,950.00
$3,150.00
$3,350.00
$3,550.00
$3,750.00
$3,950.00
$4,150.00
$4,350.00
$-
$-

Thanks for your help!!

 

[Bob Bridges]

G, I must be missing something. If you get paid 50% of your investment
immediately and the other 50% halfway through, then surely you have your
total investment back after term/2 days. That of course is 'way too simple
to need to ask about.

The next most likely scenario I can think of is this: You're investing 50%
of <amt> up front, and someone starts making regular payments back to you,
once a period for <n> periods. Halfway through the agreed number of periods
you invest the other 50% of your agreed investment. You're asking how to
calculate <n>. But that doesn't work either, for any calculation like that
includes interest, and you didn't mention it.

So can you rephrase the question?