In this guide
Build the example from the totalsCompare the tempting shortcutDefine the boundary of the summaryKeep historical and current rates separateDo not use the average to invent a service priceAn average is a summary of a set of purchases. If the purchases contain different credit quantities, the summary should reflect those quantities. Averaging two displayed rates as if the packages were equally sized can hide the purchase mix.
A labelled example combines one published 120-credit package and one 300-credit package. The example illustrates internal cost arithmetic, not a required accounting method.
Build the example from the totals
The 120-credit package costs USD 178.80 and the 300-credit package costs USD 417.00. Together they represent 420 purchased credits at a combined package cost of USD 595.80. Dividing 595.80 by 420 gives approximately USD 1.4186 per purchased credit. The larger 300-credit purchase contributes more weight to the result.
Compare the tempting shortcut
The simple average of the displayed rates, 1.49 and 1.39, is 1.44. That calculation gives each package one vote. It would be appropriate only for a different question about the average of those two labels, not the combined cost per purchased credit. The quantity-weighted calculation answers the operational question because it uses both the money spent and the credits acquired.
Define the boundary of the summary
The result covers only those two published package costs. Actual exchange charges, payment fees or other expenses are not automatically included. Nor does the average establish how a business should report inventory or cost of sales. Keep your internal calculation labelled and ask an appropriate adviser about formal reporting where needed. A useful operational number should not claim more authority than its inputs support.
Keep historical and current rates separate
A later package may have a different published rate or a specific quote. Do not overwrite the historical receipt to match the newest table. Record the actual purchase and date, then update whichever internal summary you use according to its defined method. Otherwise a retrospective calculation can pretend that an earlier purchase cost less than it actually did.
Do not use the average to invent a service price
Even a correct purchased-credit average needs a confirmed consumption quantity before it can contribute to an action-cost calculation. Customer price, fees and other expenses are additional inputs. If one is missing, leave that part open. The weighted average is valuable because it preserves the purchase mix, not because it turns a credit balance into a guaranteed resale result.
Keep purchase quantity and purchase cost together when moving the data between tools. Copying only the two unit rates loses the weights needed to reproduce the calculation. A reviewer should be able to return to the actual receipts and see why the larger package contributes more to the result. This is particularly useful when a later purchase joins the mix.
Questions about this guide
Why is the result closer to USD 1.39 than USD 1.49?
The 300-credit purchase contributes more credits than the 120-credit purchase, so it has more weight in the combined per-credit result. The calculation uses total cost divided by total quantity. It does not give every package equal weight regardless of size.