Blog
Worked examples and the real math behind ExactCalcs' calculators — no generic filler, every number cited or computed.
- How much extra should you pay on your mortgage to pay it off a year early?
The extra monthly amount that shaves a year off a mortgage, with real numbers at 6.5% and 30 years.
- Rent vs. buy: how many years until buying actually wins?
The break-even year where a home purchase beats renting, and the assumptions that move it by years in either direction.
- How many months of expenses should an emergency fund actually cover?
3 months, 6 months, or something else — how to size an emergency fund to real, variable monthly expenses instead of a rule of thumb.
- SaaS burn rate and runway: how many months of cash do you actually have?
How runway is actually calculated from cash, burn rate, and revenue growth — and why a single burn-rate number understates risk.
- Solar panel payback period: how many years until they pay for themselves?
The payback-period math behind a solar quote, and the three inputs that move it more than panel efficiency does.
- How much should you actually tip on a $60 bill?
What 15%, 18%, 20%, and 25% come out to on a $60 check, split evenly, and why the "always 20%" rule is newer than it feels.
- Debt snowball vs. avalanche: which one actually pays off debt faster?
The real interest-cost gap between paying off smallest balances first versus highest interest rates first, with a worked example.
- What does leaving a space heater on all day actually cost?
The real dollar cost of running a 1500W space heater for 8, 12, or 24 hours, at typical US electricity rates.
- How long until your BAC is back to 0.00?
The Widmark-formula math behind how long alcohol actually takes to clear your system, and why 'one drink per hour' is a rough floor, not a guarantee.
- How much extra should you pay on a car loan to pay it off a year early?
The extra monthly payment that cuts a year off a typical car loan, and how much interest that actually saves.