Side by Side Calc
Eight money decisions worked out both ways: rent vs buy, refinance vs keep your loan, 15 vs 30-year, lease vs finance a car, Roth vs traditional, ARM vs fixed, HSA vs PPO, and EV vs gas -- each with a real verdict, a break-even point, and the numbers shown.
Every tool below runs two scenarios side by side and ends in one line: which side wins, and by how much. Most have a break-even year -- the point where the answer flips -- and a slider so you can feel how much the verdict depends on the number you're least sure about.
Eight money decisions
Every tool below runs two scenarios side by side and ends in one line: which side wins, and by how much. Most have a break-even year -- the point where the answer flips -- and a slider so you can feel how much the verdict depends on the number you're least sure about.
BuyingvsRenting
Rent vs Buy
Whether owning beats renting once you count the down payment you didn't invest and the equity you built.
Current loanvsNew loan
Refinance Break-Even
How many months of lower payments it takes to earn back what refinancing costs you upfront.
15-yearvs30-year
15 vs 30 Year
The 15-year's forced savings against the 30-year's lower payment invested at your own rate.
BuyingvsLeasing
Lease vs Buy a Car
Total cost of leasing against financing and keeping the car, resale value included.
RothvsTraditional
Roth vs Traditional
Tax-free later against a deduction now, plus the same-take-home comparison most calculators skip.
ARMvsFixed
ARM vs Fixed
A lower introductory ARM rate against a fixed rate that never resets, at how long you'll actually stay.
HSA planvsPPO plan
HSA vs PPO
A high-deductible plan's tax-advantaged savings against a PPO's lower deductible, at your real medical spend.
EVvsGas
EV vs Gas
A higher sticker price and lower running cost against gas's cheaper purchase and pricier fuel.
Prediction market math
The arithmetic behind trading YES/NO contracts: converting odds, pricing your edge, sizing a bet, and checking whether an arbitrage is real once fees are counted.
Odds Converter
American, decimal, and fractional odds, implied probability, and contract price (¢) -- one number, every format.
YES pricevsNO price
Implied Probability
What a single price or odds quote implies about the odds, and what a market's two prices say about its built-in vig.
Your estimatevsMarket price
Expected Value
Whether your probability estimate beats the market's price, and by how much per contract and per $100.
Kelly Criterion
How much of your bankroll an edge actually justifies staking -- and when the honest answer is zero.
CostvsPayout
Payout Calculator
What a YES or NO position actually costs and pays, contracts and fees included.
Venue A (YES)vsVenue B (NO)
Arbitrage Calculator
Whether opposite positions across two venues (or the two sides of one market) lock in a guaranteed profit.
Frequently Asked Questions
How is this different from a regular calculator?
Most calculators give you one number for one scenario. Every tool here runs two scenarios side by side, from the same shared assumptions, and ends in a single verdict: which one wins, and by how much. Each one also has a sensitivity control so you can see how much the verdict depends on the one input you're least sure about.
Where do the formulas come from?
Standard, published finance formulas: loan amortization for every mortgage and auto-loan calculator, future-value-of-annuity math for invest-the-difference comparisons, and deductible/coinsurance cost-sharing math for the health-plan comparison. The prediction-market tools use the same standard of published, well-known math: odds/probability conversions, the Kelly criterion, and fetched, cited fee schedules rather than assumed ones. Every calculator's page names its method and shows the arithmetic.
Is this financial advice?
No. These are estimates for comparing two paths given the numbers you enter, not tax, legal, or investment advice, and the prediction-market tools are not trading advice. Real decisions involve details -- your specific loan terms, plan documents, state rules, or a market's actual rules -- these calculators can't see. Use them to understand the shape of a decision, then confirm specifics with a professional. Prediction markets carry real risk of loss and may be restricted in some jurisdictions.