Extension Durations

This is how long Extension will extend castings for, based on relative levels. It also applies to Extend.

Self: You are applying Extend/Extension to your own casting.
Other: You are applying Extend/Extension to someone else’s casting.
Opposite: You are applying Extension to a miracle or Extend to a spell, i.e. the opposite type of casting.

Downcasting is dropping the level of a fifteen-minute casting while casting it to increase its duration. The difference is based on effect levels, not absolute spell levels – see the Downcasting rules for details.

Relative Extension to Casting Level				Downcasting			Duration
Self	Other	Self-Opposite	Other-Opposite		Hours	Days	Years
0	+1	+2	+3	-1	1
+1	+2	+3	+4	-2	4
+2	+3	+4	+5	-3	16
+3	+4	+5	+6	-4	64	2
+4	+5	+6	+7	-5	256	10
+5	+6	+7	+8	-6	1024	42
+6	+7	+8	+9	-7	4096	170
+7	+8	+9	+10	-8	16384	682	2
+8	+9	+10	+11	-9	65536	2730	7
+9	+10	+11	+12	-10	262144	10922	30
+10	+11	+12	+13	-11	1048576	43690	120

Note: Yes, the maths for calculating days and years is slightly dodgy, but it matches Tony’s maths in another, similar chain.