Good Day
I have noticed that when running an Provisional Bill from 20 September until 20 October, the KVa rate is not the same as in the Tariff.
It is displaying R144.9763 per KVa and not R148 / KVa.
Can you please tell me why this is?:confused:

Good Day
The best would be is to run the bill from the 1st to the first.
As soon as you start running from any other date as the first to the first it starts getting complex.
The KVa is calculated in pro-rata per month, as follows:
Rate per kVa (as set in the Tariff) divided by the days in September times the days left in September, equals the pro-rata rate for September.
148 / 30 * 11 = 54.266666666667
Rate per kVa (as set in the Tariff) divided by the days in October times the days already in October, equals the pro-rata rate for October
148 / 31 * 19 = 90.709677419355
And if you add the two pro-rata rates together, it equals the rate as set in the Tariff:
90.7096 + 54.2666 = 144.9762
I do hope that this clarifies it.

Just to prove that this does work out to an average of R148/kVA over a year period, consider the following:
Jan-Feb
148/31*12=57.290322580645
148/28*19=100.42857142857
Feb-Mar
148/28*09=47.571428571429
148/31*19=90.709677419355
Mar-Apr
148/31*12=57.290322580645
148/30*19=93.733333333333
Apr-May
148/30*11=54.266666666667
148/31*19=90.709677419355
May-Jun
148/31*12=57.290322580645
148/30*19=93.733333333333
Jun-Jul
148/30*11=54.266666666667
148/31*19=90.709677419355
Jul-Aug
148/31*12=57.290322580645
148/31*19=90.709677419355
Aug-Sep
148/31*12=57.290322580645
148/30*19=93.733333333333
Sep-Oct
148/30*11=54.266666666667
148/31*19=90.709677419355
Oct-Nov
148/31*12=57.290322580645
148/30*19=93.733333333333
Nov-Dec
148/30*11=54.266666666667
148/31*19=90.709677419355
Dec-Jan
148/31*12=57.290322580645
148/31*19=90.709677419355
For each month, the kVA would calculate to:
57.290322580645+100.42857142857=157.71889400921
47.571428571429+90.709677419355=138.28110599078
57.290322580645+93.733333333333=151.02365591398
54.266666666667+90.709677419355=144.97634408602
57.290322580645+93.733333333333=151.02365591398
54.266666666667+90.709677419355=144.97634408602
57.290322580645+90.709677419355=148
57.290322580645+93.733333333333=151.02365591398
54.266666666667+90.709677419355=144.97634408602
57.290322580645+93.733333333333=151.02365591398
54.266666666667+90.709677419355=144.97634408602
57.290322580645+90.709677419355=148
And if you summate all the rates:
57.290322580645+100.42857142857+47.571428571429+90.709677419355+57.290322580645+93.733333333333+54.266666666667+90.709677419355+57.290322580645+93.733333333333+54.266666666667+90.709677419355+57.290322580645+90.709677419355+57.290322580645+93.733333333333+54.266666666667+90.709677419355+57.290322580645+93.733333333333+54.266666666667+90.709677419355+57.290322580645+90.709677419355=1776
Then divide by 12 months:
1776/12=148
You get exactly R148/kVA!

Please note, that the Prorata checkbox on the Maximum Demand tariff line item is entirely optional. You can simply remove that checkbox, and the tariff will be applied in the normal way.
What it means if you add the prorata checkbox, is that any period you select that is not precisely 1 month will mean that the cost is adjusted, accordingly. For instance, the 20th of February in a non leap year to 20 March, would be 9/28 month + 19/31 month = 92.3248% of a month, not 1 month.
Usually the pro-rata chechbox should be used for places that charges customers for periods that are less (or more) than a month, e.g. studios and soccer stadiums.
To see correct Provisional Months over e.g. a year, rather use the option on the meter account to chop up bills between official Billing Periods, as you can set up per meter account.