Fixed vs variable mortgage calculator
Initial rates, reset paths, term, and balance to cumulative cost under rate scenarios.
Model each structure under stable, gradual, faster, reversal, and severe rate paths to see the monthly payment, balance, and cumulative interest — so you choose variable only if you survive the stress paths.
Key points
- Compares fixed and variable under five rate scenarios.
- Shows monthly payment, balance, and cumulative interest for each.
- Models the contract’s payment-reset and unpaid-interest rules.
- Choose variable only if you survive the +2 to +3 point paths.
Inputs and outputs
Inputs: fixed and variable initial rates, term, balance, and a rate path — stable (no change), gradual (+0.25/12mo for four years), faster (+0.50/year for four years), reversal (+1.50 then partial decline), or severe (+2 immediately, later +1).
Outputs: for each structure and path, the monthly payment, balance, and cumulative interest, modeling the actual contract’s reset rules and any unpaid-interest treatment.
How to interpret the result
The calculator is only as good as the rate paths you test; a household that fails the +2 to +3 point paths should not choose variable.
What the tool shows — and what it doesn’t
In short: Compares fixed and variable under five rate scenarios; Shows monthly payment, balance, and cumulative interest for each; Models the contract’s payment-reset and unpaid-interest rules; Choose variable only if you survive the +2 to +3 point paths.
A calculator is only as good as its inputs and the scenarios you test, and it models arithmetic, not approval: it cannot tell you whether a lender will lend, what rate underwriting will actually offer, or how your circumstances will change. Use it to compare options and to stress-test — run a mortgage at the offered rate plus one, two, and three points, and a purchase at pessimistic as well as central assumptions — rather than to produce a single answer. Advertised rates are execution-month or example figures, not guaranteed offers, so treat any result as a planning estimate and confirm the real numbers with a dated written quotation before you commit.
Who this is for
- Buyers and borrowers modeling a decision
- Anyone stress-testing affordability
What this is not
- A guaranteed quote or approval
- The calculator is only as good as the rate paths you test; a household that fails the +2 to +3 point paths should not choose variable.
Frequently asked questions
Fixed or floating mortgage rate in Japan — which is better?
There is no universal answer. Floating rates (変動) have been lower and reduce early payments but can rise, increasing your payment later. Fixed rates (固定, including Flat 35) cost more now but lock certainty for the term, protecting you if rates rise. Choose based on how much payment-increase risk you can absorb: if a rate rise would strain your budget, the certainty of fixed can be worth the premium. Model both before deciding.
Are variable rates risky?
Yes, especially when affordability depends on the starting rate. Choose variable only if you survive a 2–3 point rise without selling.