Find the lower combined bill for a married couple.
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When pooling two incomes helps, and when it does not
A married couple in Hong Kong can be taxed two ways. Under separate taxation each spouse files on their own income and claims their own basic allowance. Under joint assessment the two incomes are combined, the married person's allowance is applied to the pair, and the couple is taxed as one unit. This calculator runs both computations and shows the lower bill, which is exactly what the Inland Revenue Department does in practice: it only grants joint assessment if it actually reduces the couple's total tax. The tool is for couples wondering whether to elect joint assessment, especially where one partner earns far less than the other.
The short version of the logic: joint assessment helps when one spouse cannot fully use their own basic allowance, because pooling lets the higher earner soak up the unused relief. When both earn enough to use their allowances and lower bands separately, the two methods usually come out the same, since the allowances and progressive bands are designed to line up.
How each side is computed
Salaries tax is the lower of progressive rates on net chargeable income, after allowances, and the standard rate on net total income, before allowances, with a one-off Budget reduction applied at the end. Under separate assessment the calculator gives each spouse their own basic allowance, the figure modelled here being $132,000, and works out each bill independently. Under joint assessment it combines the incomes, applies the married person's allowance, $264,000 in this model, plus any child allowances, and computes one bill. Treat the $132,000 and $264,000 allowance figures and the one-off reduction as the calculator's assumptions for the modelled year, and confirm the current allowances and any concession with the Inland Revenue Department.
One high earner, one low earner: the classic case
Run the defaults. Spouse A earns $600,000 with $18,000 of deductions; Spouse B earns $120,000 with $6,000 of deductions; no children are claimed. Under separate assessment, Spouse A's net chargeable income after the $132,000 basic allowance is $450,000, producing tax of $58,500 before a $3,000 reduction, so $55,500. Spouse B's income after deductions is $114,000, which is below the $132,000 basic allowance, so the net chargeable income is nil and the tax is zero. The separate total is $55,500, and crucially $18,000 of Spouse B's basic allowance goes to waste. Under joint assessment the combined net total income is $696,000, the married allowance of $264,000 leaves $432,000 chargeable, the tax is $55,440 before the $3,000 reduction, so $52,440. Joint assessment wins by $3,060.
The $3,060 saving is no coincidence. It is roughly the unused slice of Spouse B's allowance taxed at the higher earner's rate, recovered by pooling. If Spouse B earned enough to use the full $132,000 allowance, the two columns would converge.
Subtleties the comparison surfaces
Two details deserve a flag. First, the one-off Budget reduction is capped per case, and under joint assessment a couple shares a single cap rather than getting one each, which slightly erodes the benefit of going joint. The calculator handles this by applying the reduction once to the joint bill and once to each separate bill. Second, joint assessment is an all-or-nothing election for the couple; you cannot pick and choose which income to pool. Hong Kong taxes only the spouses' employment and business income here, with no joint taxation of investment returns, because there is no tax on dividends, savings interest, or capital gains to combine in the first place.
A practical tip: you do not have to gamble. Because the IRD applies whichever basis is lower once you elect joint assessment, electing it does no harm when separate would have been better, as the department defaults you to the cheaper outcome. But you must make the election in time, so check the deadline on your return rather than assuming it is automatic.
Does adding children change which method wins?
Child allowances are claimed by one spouse, usually the higher earner, under either method, so they do not by themselves tip the balance between joint and separate. What still drives the decision is whether the lower earner's basic allowance is going unused. Enter the number of children in the tool to see the combined bill, but expect the join-or-separate gap to hinge on the income split, not the kids.
Is personal assessment the same as joint assessment?
No, they are different elections. Joint assessment pools a married couple's income under salaries tax. Personal assessment is a separate mechanism, mainly useful for people with business or rental income, that lets you aggregate income across tax types and claim certain deductions against the lot. A couple can sometimes benefit from electing personal assessment jointly, but that is a wider calculation than this tool runs, so check it with the IRD if you have non-salary income.