## A powerful tool for a silly thing.  Why not?  🙂

Long time ago, I wrote a blog post How much do I need to pay? which was not really related to Excel but calculation of a random daily event.   Similar to that old story, a friend asked me for an Excel solution for a different scenario, which I think is quite interesting and really need Excel to do the calculation.

Long story short – when we have more than one birthday stars in a party, maybe a birthday star should treat other birthday star(s) as well.  Thus, s/he will need to pay a share.  WOW… it sounds like an Excel challenge that I really like to take.

Here’s my solution:

Here’s an online version which you may input the valuables directly.  Hope you like it! 🙂

### Background Story

Indeed there was a real situation that triggered his idea of requesting this Birthday Treat Calculator.  On birthday dinner gathering, birthday star doesn’t have to pay as the rest of the group would love to treat him/her dinner.  Then one day in a birthday gathering, there was three birthday stars out of six people.  Turned out that three people paid the bill for six.  It is not a problem at all as we are good friend; and we know it takes turn to treat each other.  It is a zero-sum event, more or less.

Then one day, he asked when we have more than one birthday stars in a gathering, shall birthday stars treat other birthday star(s) as well?  Interesting! That’s the reason of this post.

### Calculation Logic

Honestly, it took me a while sitting quietly to figure out the calculation logic.  Instead of working on Excel spreadsheet, I needed a pen and pencil to draft the calculation steps.

The bottleneck was how to determine the share by a birthday star when there is more than one even 2, 3, 4, etc….  birthday stars.  Then all a sudden the following came to my mind:

 Every participant is responsible for a share; the rest of the group simply splits that birthday star’s share and takes it.

And that is the key of the solution.

You may download the Birthday Treat Calculator – Desktop version, where I have put step-by-step calculation on the worksheet <Logic>.  Feel free to examine it and reverse-engineer it.

Please tell me what you do think about it? Will you really use it? I mean asking birthday stars to clip in… 😛

p.s. I am using a simple logic for the calculation.  If you have a more sophisticated (and more accurate) approach to do this calculation, please share with us.  🙂