66/33 vs 50/50 split (UK)

Quick intuition: what are you optimizing?

Most couples are optimizing for one (or more) of these: (1) both people keep a similar leftover, (2) both people feel the contribution is reasonable, and (3) the plan still works if rates rise or one income drops.

Proportional splits are often best for (1). 50/50 is best for symmetry and simplicity. A custom split like 66/33 is best when you want a stable rule that’s “close enough” and avoids constant recalculation.

When 66/33 makes sense

• Your incomes are roughly 2:1 and you don’t expect them to swing monthly.
• You want a simple rule you can explain and repeat (especially early on).
• You’ve agreed a longer-term “story” (e.g. one person paid a larger deposit).

When to avoid 50/50

If 50/50 leaves one person with very little leftover, you’ll feel it quickly. It can create anxiety, resentment, or pressure to overwork. The calculator’s “leftover each” is the fastest sanity check.

A simple decision checklist

• Pick a split that both people can repeat without friction (50/50, proportional, or a fixed custom split like 66/33).
• Check leftovers for both people — if one leftover is consistently “tight”, it will show up in day‑to‑day decisions.
• Run the stress tests (+1% / +2% and one‑income). If it breaks, lower the house price or raise the deposit.
• If you want a method that automatically tracks income changes, use proportional by income.