iliace
Well-known Member
- Joined
- Jan 15, 2008
- Messages
- 3,562
- Office Version
- 365
- Platform
- Windows
Hi all,
This is more of a math question than an Excel question, but hopefully some folks have a solution and enough people are interested.
Here is the situation, as simplified/generalized as I can make it.
I have clients that pay a contractual periodic fee. It is a dollar amount, but can also be expressed as a percentage of the client's (own) business volume.
I take an average "effective" rate for a group of clients.
I forecast client fees I collect periodically.
The following three types of events can occur in-between any two forecasts:
- A client leaves (e.g. contract ends, breach of contract, etc)
- A new client comes onboard
- A client renews his or her contract
New clients generally have incentives (lower fees) at the beginning of their contract period, and over the life of the contract they are increased up to the full amount. Therefore, clients leaving were generally paying higher fees than new clients coming onboard will be paying. A similar situation happens with renewals: to give an existing client incentive to renew, they are typically offered a discount. However, this is not always the case; sometimes renewals and new clients have higher rates than existing clients or those exiting. The net result is, the effective (weighted average) rate of the total client portfolio changes from one point in time to another in the future.
What I'm after is the amount each category of events contributes to the percentage change in the overall effective rate in the later of the two forecasts. Here is an example of what we might have. I know that the effective rate went down from 3.9068% to 3.7555% (15.138 bps). What I'm after is the column E - the number of basis points by which each category of change contributed to the decrease in the overall effective rate. In other words, how many of the 15.138 bps was each component, in bps.
Removing each component and comparing the ending rate works to an extent, but because the relative weight of each remaining component changes, this is not precise (overestimates). Adding each component individually and comparing it to the beginning rate has the opposite problem (underestimates). Taking the midpoint between the two gets pretty close. I am quite content with this approximation for calculation purposes, but it is difficult to explain. And as we know, when you can't explain something convincingly, people have a much harder time relying on it, and I am foreseeing a time when someone might press for details of "exactly how did you get that number".
Right now, I have a formula (sum of E5:E8) that gets very close to the actual result (D12) but not precisely: 15.136 instead of 15.138.
(1) I am wondering whether this approach is logically valid. It makes sense in my head, but I am no mathematician and I may not be grasping a nuance.
(2) I am wondering if there is a way to make this calculation precisely, or even "properly", in such a way as to refer to some kind of theorem or rule. Something that sounds along the lines of "The Riemann-Gauss Approximation" would be great.
<tbody>
[TD="bgcolor: #cacaca, align: center"]3[/TD]
[TD="align: center"]Business Volume[/TD]
[TD="align: center"]Client Fee[/TD]
[TD="align: center"]Effective Rate[/TD]
[TD="align: center"]Contribution[/TD]
[TD="bgcolor: #cacaca, align: center"]4[/TD]
[TD="align: right"]$500,000.00[/TD]
[TD="align: right"]$19,534.23[/TD]
[TD="align: right"]3.9068%[/TD]
[TD="bgcolor: #cacaca, align: center"]5[/TD]
[TD="align: right"]($5,000.00)[/TD]
[TD="align: right"]($210.48)[/TD]
[TD="align: right"]4.2095%[/TD]
[TD="align: right"]-0.377%%[/TD]
[TD="bgcolor: #cacaca, align: center"]6[/TD]
[TD="align: right"]$9,000.00[/TD]
[TD="align: right"]$222.78[/TD]
[TD="align: right"]2.4753%[/TD]
[TD="align: right"]-2.433%%[/TD]
[TD="bgcolor: #cacaca, align: center"]7[/TD]
[TD="align: right"]($500.00)[/TD]
[TD="align: right"]($638.75)[/TD]
[TD="align: right"]127.7501%[/TD]
[TD="align: right"]-12.361%%[/TD]
[TD="bgcolor: #cacaca, align: center"]8[/TD]
[TD="align: right"]($1,000.00)[/TD]
[TD="align: right"]($36.57)[/TD]
[TD="align: right"]3.6568%[/TD]
[TD="align: right"]0.035%%[/TD]
[TD="bgcolor: #cacaca, align: center"]9[/TD]
[TD="bgcolor: #cacaca, align: center"]10[/TD]
[TD="align: right"]$502,500.00[/TD]
[TD="align: right"]$18,871.22[/TD]
[TD="align: right"]3.7555%[/TD]
[TD="align: right"]-15.136%%[/TD]
[TD="bgcolor: #cacaca, align: center"]11[/TD]
[TD="bgcolor: #cacaca, align: center"]12[/TD]
[TD="align: right"]Total Change[/TD]
[TD="align: right"]15.138%%[/TD]
</tbody>
<tbody>
</tbody>
This is more of a math question than an Excel question, but hopefully some folks have a solution and enough people are interested.
Here is the situation, as simplified/generalized as I can make it.
I have clients that pay a contractual periodic fee. It is a dollar amount, but can also be expressed as a percentage of the client's (own) business volume.
I take an average "effective" rate for a group of clients.
I forecast client fees I collect periodically.
The following three types of events can occur in-between any two forecasts:
- A client leaves (e.g. contract ends, breach of contract, etc)
- A new client comes onboard
- A client renews his or her contract
New clients generally have incentives (lower fees) at the beginning of their contract period, and over the life of the contract they are increased up to the full amount. Therefore, clients leaving were generally paying higher fees than new clients coming onboard will be paying. A similar situation happens with renewals: to give an existing client incentive to renew, they are typically offered a discount. However, this is not always the case; sometimes renewals and new clients have higher rates than existing clients or those exiting. The net result is, the effective (weighted average) rate of the total client portfolio changes from one point in time to another in the future.
What I'm after is the amount each category of events contributes to the percentage change in the overall effective rate in the later of the two forecasts. Here is an example of what we might have. I know that the effective rate went down from 3.9068% to 3.7555% (15.138 bps). What I'm after is the column E - the number of basis points by which each category of change contributed to the decrease in the overall effective rate. In other words, how many of the 15.138 bps was each component, in bps.
Removing each component and comparing the ending rate works to an extent, but because the relative weight of each remaining component changes, this is not precise (overestimates). Adding each component individually and comparing it to the beginning rate has the opposite problem (underestimates). Taking the midpoint between the two gets pretty close. I am quite content with this approximation for calculation purposes, but it is difficult to explain. And as we know, when you can't explain something convincingly, people have a much harder time relying on it, and I am foreseeing a time when someone might press for details of "exactly how did you get that number".
Right now, I have a formula (sum of E5:E8) that gets very close to the actual result (D12) but not precisely: 15.136 instead of 15.138.
(1) I am wondering whether this approach is logically valid. It makes sense in my head, but I am no mathematician and I may not be grasping a nuance.
(2) I am wondering if there is a way to make this calculation precisely, or even "properly", in such a way as to refer to some kind of theorem or rule. Something that sounds along the lines of "The Riemann-Gauss Approximation" would be great.
A | B | C | D | E | |
Forecast 1 | |||||
Clients Leaving | |||||
New Clients | |||||
Renewal (net) | |||||
Other Change | |||||
Forecast 2 | |||||
<tbody>
[TD="bgcolor: #cacaca, align: center"]3[/TD]
[TD="align: center"]Business Volume[/TD]
[TD="align: center"]Client Fee[/TD]
[TD="align: center"]Effective Rate[/TD]
[TD="align: center"]Contribution[/TD]
[TD="bgcolor: #cacaca, align: center"]4[/TD]
[TD="align: right"]$500,000.00[/TD]
[TD="align: right"]$19,534.23[/TD]
[TD="align: right"]3.9068%[/TD]
[TD="bgcolor: #cacaca, align: center"]5[/TD]
[TD="align: right"]($5,000.00)[/TD]
[TD="align: right"]($210.48)[/TD]
[TD="align: right"]4.2095%[/TD]
[TD="align: right"]-0.377%%[/TD]
[TD="bgcolor: #cacaca, align: center"]6[/TD]
[TD="align: right"]$9,000.00[/TD]
[TD="align: right"]$222.78[/TD]
[TD="align: right"]2.4753%[/TD]
[TD="align: right"]-2.433%%[/TD]
[TD="bgcolor: #cacaca, align: center"]7[/TD]
[TD="align: right"]($500.00)[/TD]
[TD="align: right"]($638.75)[/TD]
[TD="align: right"]127.7501%[/TD]
[TD="align: right"]-12.361%%[/TD]
[TD="bgcolor: #cacaca, align: center"]8[/TD]
[TD="align: right"]($1,000.00)[/TD]
[TD="align: right"]($36.57)[/TD]
[TD="align: right"]3.6568%[/TD]
[TD="align: right"]0.035%%[/TD]
[TD="bgcolor: #cacaca, align: center"]9[/TD]
[TD="bgcolor: #cacaca, align: center"]10[/TD]
[TD="align: right"]$502,500.00[/TD]
[TD="align: right"]$18,871.22[/TD]
[TD="align: right"]3.7555%[/TD]
[TD="align: right"]-15.136%%[/TD]
[TD="bgcolor: #cacaca, align: center"]11[/TD]
[TD="bgcolor: #cacaca, align: center"]12[/TD]
[TD="align: right"]Total Change[/TD]
[TD="align: right"]15.138%%[/TD]
</tbody>
Formeln der Tabelle | ||||||||||||||||
<tbody> </tbody> |
<tbody>
</tbody>
Last edited: