Percentage change in Excel: increases, decreases and a zero starting value

Choose the starting value before calculating

A workshop had 80 bookings in April and 100 in May. Put April in B2 and May in C2. The change is 20 bookings. To express that change relative to April, divide 20 by the April value of 80.

This example uses non-negative counts and a positive starting value for the ordinary percentage calculation. It is not a rule for interpreting negative profits or balances.

Subtract the original, then divide by the original

The formula returns 0.25. Apply percentage formatting in a workbook to display 25%. The practice result below shows the raw decimal so you can see the value used in later calculations.

=(C2-B2)/B2

An increase and its reversal have different percentages

Going from 80 to 100 is an increase of 20 on a base of 80: 25%. Going from 100 back to 80 is a decrease of 20 on a base of 100: -20%. The absolute change has the same size, but the denominator is different.

Dividing the increase by the new value would also produce 20%, but it would answer a different question. Keep the original period as the denominator when reporting change relative to that period.

Do not multiply twice

Percentage formatting displays 0.25 as 25%. If you calculate 25 by multiplying by 100 and then apply percentage formatting, the display becomes 2500%. Keep the decimal result when the cell will use percentage formatting.

A zero change is different from an undefined change. If both periods have 80 bookings, the formula returns 0, which displays as 0%.

Handle a zero starting value explicitly

The new workshop grew from 0 to 20 bookings. It gained 20 bookings, but an ordinary percentage change relative to zero is undefined. Showing 0% would falsely suggest no change; showing 100% would also be misleading.

Use an explicit message for a zero base, and report the absolute change separately. The same message is returned if both values are zero because the percentage formula still has a zero denominator.

=IF(B4=0,"No percentage base",(C4-B4)/B4)

Percentages are not percentage points

If a booking conversion rate moves from 20% to 25%, it rises by 5 percentage points. Relative to the original rate, the increase is 5 / 20 = 25%. Label the measure so readers know which one you mean.

Do not average percentage changes across branches unless that weighting is intentional. To report the overall change in bookings, add the original counts and new counts first, then calculate the change from those totals.

Check the inputs before publishing

Both periods should cover comparable durations and the same definition of a booking. A missing value is not automatically a zero, so review blanks before calculating.

In the practice table, change C2 from 100 to 80: the result becomes 0. Change it to 60: the result becomes -0.25. These checks distinguish no change from a decrease without changing the denominator.

Further reading

• Microsoft: calculate percentage increases and decreases