D.C. Mun. Regs. tit. 9, r. 9-146
A joint declaration may be made by husband and wife, in which case liability with respect to estimated tax shall be joint and several.
No joint declaration may be made if the husband and wife are separated under a decree of divorce or of separate maintenance, or if they have different taxable years.
If a joint declaration is made, but a joint return is not made for the taxable year, the estimated tax for that year may be treated as the estimated tax of either husband or wife, or may be divided between them.
The making of a joint declaration does not require the husband and wife to file a joint final return. However, if a husband and wife make separate declarations, they cannot file a joint return.
If a joint declaration is made but separate returns are made for the taxable year, the estimated tax for that year may be treated as the estimated tax of either the husband or the wife or may be divided between them in any proportion they may choose.
D.C. Mun. Regs. tit. 9, r. 9-146