If you and your partner didn't put in the same deposit, "half each" isn't the truth. This works out each person's real share of the equity — value minus mortgage, divided the way you actually agreed.
Free, no signup, and nothing leaves your browser — the arithmetic runs on your device and nothing is sent to us or stored.
The last field is for a property only partly owned by your household — a place bought with a parent, or held through a company. Leave it at 100 if the two of you own all of it.
The instinct is to split the house price and worry about the mortgage separately. That produces a number that is far too flattering, and it moves for the wrong reasons — a £40,000 valuation bump looks like a £40,000 gain when the debt behind it hasn't moved at all.
Equity is value minus mortgage. Split that, and each person's figure behaves like an asset they actually hold: it rises when the house rises and when the mortgage falls, and the two shares always add back to the household total.
There is no formula, and anyone who gives you one is guessing at your arrangement. In practice couples use one of three:
| Deposit-proportional | Each person's share reflects what they put in at purchase. Simple, and the most common starting point. |
|---|---|
| Deposit plus contributions | Deposits, then mortgage payments and major works tracked over time. Fairer, more work, and it changes as you go. |
| Agreed and fixed | A number you both settled on for your own reasons, written down and left alone. |
This has no legal effect. A percentage here describes what you believe you own. If you want it to bind — on separation, death, or a sale — that is a declaration of trust, drawn up by a solicitor, and it is not expensive relative to what it protects. Worth doing if the split is meaningfully uneven.
In England and Wales, unequal shares are what a tenants in common arrangement is for: each owner holds a defined percentage — 60/40, 75/25, whatever was agreed — usually recorded in a deed of trust (also called a declaration of trust). That is the situation this calculator models, and it's common for unmarried couples, friends buying together, and partners contributing unequal deposits.
Joint tenants is the other arrangement: both own the whole property together with no separable shares, and it passes automatically to the survivor. If you're joint tenants, a percentage split has no legal meaning — though couples still find a notional split useful for tracking who contributed what.
One honest disambiguation: this is not a shared ownership calculator in the housing-scheme sense. Shared ownership (part-buy, part-rent through a housing association) has its own arithmetic — rent on the unowned share, staircasing costs — which this tool doesn't model. This calculator is for private co-owners splitting equity between themselves.
The number changes every month as the mortgage falls, and neither of you will recalculate it. OwnWorth holds the split permanently and applies it to value, equity, mortgage, rent and payments, so each person's view stays right without anyone doing arithmetic — how that works.
See it with an example household Section 104 calculator →
OwnWorth is a record-keeping and planning tool, not financial, legal or tax advice, and we are not regulated to give any. Figures you enter are your own; projections are estimates based on them.