I don't think it makes much difference unless one spouse is on 20% income tax and the other is on 42%. You can double check using [broken link removed] by calculating each spouse's tax liabilities separately and then as a married couple. In general it probably makes sense to be on joint aggregated assessment - if there is any advantage to be gained then that approach will provide it otherwise you will not lose out. See [broken link removed] for more on married taxation.