Do you mean something like the below..

Col A contain dates formatted to month and year. Jan-09 is in cell A3. In B3
enter the formula =IF(MOD(MONTH(A3),3)=1,B2+100,B2)

ColA ColB
Amount
Starting 1000
Jan-09 1100
Feb-09 1100
Mar-09 1100
Apr-09 1200
May-09 1200
Jun-09 1200
Jul-09 1300
Aug-09 1300
Sep-09 1300
Oct-09 1400
Nov-09 1400
Dec-09 1400
Jan-10 1500


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---------------
Jacob Skaria


"chandra1961" wrote:

i have 12 months from january to december , each month say Rs 100 as input
whenever january or april or july or october months ie every quarter i have
to increment rs 100,
for example when jan comes increment rs 100 to the cell other months no
icrement
for april comes only april incremented likewise every quarter

please reply