How to write formula that shows a "fixed" result

[matthewhinds]

To Whom It May Concern

How do I write a formula that returns a "fixed" ($) amount?

Here's an example of what I am asking...

Let's say I was paying back a credit card with a $5k limit.

I've created the following formula: =(IF(Totals!$B$4=0, "", (IF(Totals!$B$4<=5000, Totals!$B$4*4.207%, Totals!$B$4*8.414%))))
[NB Totals!B4=(SUM(Totals!B2:B3))]

Now, the amount I pay (fortnightly), is ='Regular Expenses'!$B$6.
[ie 'Regular Expenses'!$B$6=(IF(Totals!$B$4=0, "", (IF(Totals!$B$4<=5000, Totals!$B$4*4.207%, Totals!$B$4*8.414%))))]
[NB Totals!B5=(IF(Totals!$B$4=0, "", Totals!$B$4-'Regular Expenses'!$B$6))))]

Based upon this formula, every time a payment is made, the ($) amount (as shown in 'Regular Expenses'!$B$6'), will recalculate. If the figure shown in Totals!$B$4=5000 (exactly), then the figure shown in 'Regular Expenses'!$B$6 (should) =210.35.

As stated earlier, how do I write a formula that returns a "fixed" ($) amount? Ie I want 'Regular Expenses'!$B$6 =$210.35, regardless of (cell) Totals!B4 reducing, every time payments are made. [note: divide (/) $5000 by $210.35 = 23.76990729736154 fortnights]. So, in other words, I repay a $5k limit in just under 12 months, at fortnightly intervals.