THE URLTO PLAYBOOK / 10 GUIDES
Percentage calculations10-part series
Portions, discounts, changes, bases and rounding through examples.
Know the feature scope
Calculate portions, final discounted prices and changes in the browser. Change mode requires a positive initial value and does not automatically apply tax, compounding or accounting rules.
Series contents
10 guides- 01
Calculate discounts, percentage changes and percentage points
Work through a portion, a discounted price and a percentage change. Distinguish saved money from the final price and percent changes from percentage points, including the zero-base limitation.
- 02
Calculate a percentage portion of an amount
Portion mode finds part of a total. It differs from the amount after discount, so choose the mode first.
- 03
Distinguish savings from the final discounted price
Discount mode returns the remaining price. Labelling it as savings reverses the two values.
- 04
Calculate change relative to the initial value
Change divides the difference by the initial value. Reversing comparison changes the denominator; label the baseline period.
- 05
Why reversing a 25% increase requires a 20% decrease
Opposite changes need not have equal percentages. Compare both calculations with their different bases.
- 06
Record absolute change when the initial value is zero
A zero initial value makes the usual change denominator zero. Do not replace validation with an invented 100% increase.
- 07
Distinguish percentage points from relative rate increases
When a rate changes, show its difference and relative change separately. “1% increase” alone can be ambiguous.
- 08
Why successive 20% and 10% discounts do not total 30%
A successive discount uses a new base for the second step. Use each result as the next input.
- 09
Review decimals and final rounding in percentage results
Display and billing or accounting rounding can differ. Define when intermediate values are rounded before comparison.
- 10
Write a weekly link-activity report with a worked comparison
Build a weekly report from channel-specific short-link requests. Use illustrative comparison math, record period and test context and distinguish click changes from outcome claims.