Well it depends.
Usually, I would say on Average, if you haven’t reached “stable” relative parity by round 7… you’re in trouble.
You should be reaching for it around round 5, holding it by round 6, and trying to keep it round 7 and onwards.
Then it’s all about a SLOW push into Russia with the Germans, Keeping the DEI with Japan, blitzing off China, draining Russia, and survivng America, and trying to split the Americ an Income into both theatres.
You can make $20 LESS than the allies a turn, and it’s not a big deal, IF the allies have a sense of urgency, and are giving up transports, to take territories, and try and mess with you as quickly as possible.
THE GREATEST THREAT to the Axis Economic parity game, is the loss of the mediterranean, via Gibraltar, Morocco, etc, etc. Make sure you have a plan in place, to cock block the yanks, and brits, and cause as many problems as possible.