Hi Rachel,
The only option that is available within our refund policy set up right now is for you to manually select the dates and the amount that should be refunded if cancelled by those dates, so it would require you determining what the date is for 1 month out and then setting up the refund policy to be if cancelled by x date, you get $20 back, then adding an additional refund policy of if cancelled by x date you get $10 back and then a final refund policy of if cancelled by x date, you receive $0. So the "math" of figuring out the date has to happen outside of this refund policy area, but once you have the dates figured out, you can set up what you are looking for there.
This is a great suggestion though and I would recommend that you submit this product idea within Participate > Product Ideas for our product team to consider as a future enhancement request/other Cvent users to comment/up-vote if it would be helpful for them as well!
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Julia Plymack
Senior Customer Success Manager
Cvent
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