Incrementing a formula by more than a value of 1 when dragging down a row

[jeffdlinn]

I have an Amortization table in a sheet that has 360 rows and one of the columns shows the interest payment each month. In a separate sheet I have 30 rows which represent 30 years.

I have the following formula in one cell to sum the first 12 months of interest: =sum(Amortization!D6:D17) as expected when I drag this formula down the formula changes as expected to

=sum(Amortization!D6:D17)
=sum(Amortization!D7:D18)
=sum(Amortization!D8:D19)
=sum(Amortization!D9:D20)
, etc.
When I drag the formula instead of incrementing by one I'd like the formula to increment by 12 so it captures the next 12 months. As an example, it would look like this:
=sum(Amortization!D6:D17)
=sum(Amortization!D18:D29)
=sum(Amortization!D30:D41)
=sum(Amortization!D42:D53)
, etc.

 

[Fluff]

That's odd the google sheet should be in English

In future when asking questions about Google sheets you need to post in the General Discussion & Other Applications section of the board & also make it very clear what app you are using.