These are usually the quickest checks.

• Monthly cost: what leaves your account in each scenario.
• Cash to move: deposit, fees and tax, so you can check affordability early.
• Rent and mortgage interest: shown together so you can compare the two types of cost.
• Quick stress test: see what changes if rates, income or assumptions move.

With Shared Ownership you often pay rent on the share you do not own and a mortgage on the share you do.

Staircasing changes that mix over time — and it can be hard to compare the rent you pay with the mortgage interest you would pay if you bought more share.

This tool shows rent paid and mortgage interest paid in the same place, so you can compare them.

It also lets you plan staircasing as a chain of future scenarios, so you can compare timings (not just percentages).

It grew out of our own staircasing journey, where we needed to test what percentage was affordable at different LTVs, and whether we could increase our share without using savings.

Suggested scenarios to try:

• Rent vs interest: how the mix changes when you staircase.
• Timing: staircase now vs later to the same target %.
• Step plan: 25% → 50% → 75% → 100%, and compare different timelines.
• Buy more share vs invest more: compare staircasing against investing the monthly difference.
• Cash impact: test a staircase that uses savings vs one that uses borrowing (and see what happens to cash needed and buffers).

For each scenario, the tool can show:

• the new borrowing for that step (mortgage principal), and
• the total mortgage balance.

Mortgage product fees can be modelled as paid upfront or added to the mortgage.

Where relevant, the tool can spread fees over the initial product period to show an effective rate for comparison.

Examples you can compare without rebuilding the whole model:

• Renting: market rent as a baseline.
• Shared Ownership: rent on the unsold share, service charge, staircasing, and sell & buy (sale proceeds and selling costs).
• Buying: repayment or interest‑only, product fees, and refix assumptions.
• Investing the difference: what happens if you rent (or buy later) and invest monthly instead.
• Buy later: set Mortgage start as months from now to compare a later purchase against renting and/or investing in the meantime.

1. In Current circumstances, enter only what you know (income, rent or service charge, property value, mortgage balance and rate if you have them).
2. Add a future scenario and set Mortgage start as months from now (for example 9 or 24).
3. Use Essentials and pinned rows to keep only the rows you care about.
4. Use the stress tests, then refine numbers as you learn more.

• No sign‑in, no tracking, no ads.
• Runs locally in your browser.
• You can export and import a CSV if you want to save a copy.

This tool is here to help you compare options, not to sell you anything.

Feedback and collaborations: hello@hausofpostbau.com.

Feedback is how this tool improves: bugs, confusing rows, missing scenarios, and edge cases that real housing journeys surface.

If you find the tool useful and want to support ongoing maintenance, use the bright yellow Ko‑fi button at the top.