I consider the various categories as virtual envelopes containing money set aside for a particular purpose.
Is there a way to transfer amounts between categories? For instance, say I budget $200 for entertainment each month, but for several months I actually spend only $100, so the balance begins to accrue. So entertainment is overfunded. At the same time I budget $200 for gas, but spend $300. How do I transfer the overfunded entertainment amount to cover the underfunded gas category?