[cortesoft]

You would pay 10% of your wealth for income tax, so you could always mortgage your one property and pay the 10% of the mortgage value.

[aidenn0]

Newer editions remove the 10% option

[edit] Per the Monopoly Wikia the British edition was always a fixed amount and the US edition as well since 2008.

[bombcar]

Wait whaaaaat how come nobody told me monopoly went to flat tax!

[KMag]

Technically, the old system was a flat tax. The new system is a tax that's a flat fee. Flat tax almost always refers to a flat rate, not a flat fee.