Blog
Blog — practical math, finance and consumer notes
The arithmetic behind the headline numbers — and where it usually goes wrong.
- 7 minCredit card cashback math: when a flat 2% card beats a 5% cardA "5% cashback" card sounds obviously better than a "2% cashback" card. Run the math against your actual spending and the cheaper-looking option often wins. Here's the framework.
- 7 minWedding budget math: where the average $35,000 actually goesThe "average wedding costs $35,000" headline is real, but the breakdown by line item is where the planning either works or breaks. Here's the percentage-by-category map for 2026.
- 6 minStacked discounts: the math behind Black Friday's biggest trapRetailers love stacking percentages — "20% off, then an extra 15% at checkout" — and shoppers reliably add the two numbers in their head. Here's why that math is wrong, and what you're actually paying.
- 7 minCurrency exchange when traveling: the fees no one mentionsA $3,000 vacation can quietly cost $90–$180 extra in FX fees you never see itemized. Here's where the money leaks, and the cards and tools that plug each hole.
- 7 minThe 50/30/20 budget rule examined: does it actually work in 2026?Half your income on needs, 30% on wants, 20% on savings. The simplest budget rule in personal finance is also one of the easiest to misuse. Here's where it works, where it breaks, and how the percentages need to bend in 2026.
- 7 minInflation vs. your pay rise in 2026: the math no one is doing for youHeadline inflation has cooled. Your purchasing power probably hasn't recovered. Here's how to put real numbers to "did my raise keep up" — and why the answer depends on more than the CPI number on TV.
- 8 minRent vs buy in 2026: the 5% rule and the price-to-rent ratioThe "rent is throwing money away" cliché is wrong about half the time. The 5% rule and the price-to-rent ratio give you the actual answer for your city, your math, and 2026 mortgage rates.
- 6 minHow to actually compare two car loan offers (when the dealer is doing the math)A lower monthly payment is not a better deal. The dealer's spreadsheet knows this; most buyers don't. Here's the four numbers you should be checking before you sign anything.
- 5 minTip math that works in any country (and the cultural rules behind the numbers)A 20% tip in New York is generous. The same 20% in Tokyo is rude. Here's the practical math for tipping in 2026, and a quick framework for figuring out the right number anywhere in the world.
- 7 minCompound interest, the quiet millionaire: what a 1% difference does over 30 yearsA one-percentage-point fee on your retirement fund sounds harmless. Compounded for thirty years, it costs you a year of retirement income. Here's the math the fund prospectus didn't show.