Unique Loan Repayment calculation

Hi

I am an absolute novice with Excel (only used templates, mostly...) so please excuse if there is a simple answer to my issue which I have overlooked.

I am borrowing $2500 from a friend. I will be repaying different amounts at different times. We have agreed that I will repay the $2500 plus the interest she would have earned from her savings account on the amount loaned, 1.5% annually (which may change if rates improve before I have fully repaid her) calculated daily and paid monthly.

She is loaning me the money to help me purchase equipment needed to start a small business (a new camera for my photography business), I will be paying her back with any profit I earn until I have repaid the amount including the interest.

I am not sure if I am overthinking the situation and all it is is a simple interest calculation or if this is a more complicated issue. I am looking for a way to be able to input the amounts I have repaid and calculate the interest on the amount still outstanding until I reach a zero balance owed.

I think it's simply a FV calculation in which I would change the PV each time I make a payment, but I am not sure and would love some experienced feedback.

Any help or guidance in figuring this out is MUCH MUCH appreciated!!!

You could do it like this:

       -----A----- ---B--- -C-- --D-- ---E--- ----F---- ------------------------G------------------------
   1      Date       Pmt   APR   Int   Princ   Balance  Formulas                                         
   2   22 Jun 2010                            2,500.00  A2 and down: Input                               
   3   29 Jul 2010 188.00  1.5% 3.80  184.20  2,315.80  F2: Input                                        
   4   12 Sep 2010 158.00  3.0% 8.58  149.42  2,166.38  C3 and down: Input                               
   5   01 Nov 2010 181.00  2.2% 6.54  174.46  1,991.92  D3 and down: =ROUND(((1+C3/365)^(A3-A2)-1)*F2, 2)
   6   22 Jan 2011 132.00  2.0% 8.97  123.03  1,868.89  E3 and down: =B3-D3                              
   7   30 Mar 2011 147.00  1.8% 6.19  140.81  1,728.08  F3 and down: =F2-E3                              
   8   09 May 2011 254.00  1.5% 2.84  251.16  1,476.92                                                   
   9   31 Jul 2011 204.00  1.7% 5.72  198.28  1,278.64                                                   
  10   28 Sep 2011 170.00  1.8% 3.73  166.27  1,112.37                                                   
  11   25 Dec 2011  90.00  2.7% 7.26   82.74  1,029.63                                                   
  12   17 Mar 2012 216.00  1.4% 3.28  212.72    816.91                                                   
  13   29 Apr 2012 250.00  1.0% 0.96  249.04    567.87                                                   
  14   22 Jul 2012 224.00  1.3% 1.70  222.30    345.57                                                   
  15   06 Oct 2012 216.00  2.8% 2.02  213.98    131.59                                                   
  16   25 Dec 2012 132.43  2.9% 0.84  131.59      0.00