Latest entry · 2026-10-12
Browse the full indexTax Deductions vs Tax Credits: How Each Cuts Your Bill
A $2,000 credit and a $2,000 deduction are not remotely the same money. The exact math of each, a full worked return from income to bill, and where phase-outs and refundability change the answer.
- Guides in the archive
- 30
- Topics covered
- 26
- Median read
- 9 min
- Latest update
- 2026-10-12
The archive
30 entries-
02
Repair or Replace? The Appliance Math That Answers
A broken washing machine or fridge forces a fast decision with real money on the line. Work the repair-or-replace math with actual numbers: expected remaining life, the 50% rule and where it fails, energy savings, and total cost of each path.
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03
Big Tax Refund? What Over-Withholding Really Costs
A large tax refund feels like a win, but it usually means you lent the government money all year at 0% interest. Work the actual cost with numbers, learn where to adjust withholding, and see when a big refund is fine anyway.
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04
0% Financing That Isn’t: Deferred Interest Math
Store financing that says 'no interest for 12 months' can bill you a year of interest overnight. Here is exactly how deferred interest works, with the math of a $1,800 laptop.
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05
Sinking Funds: The Math Behind Irregular Bills
Car repairs, holidays, vet bills — the expenses that wreck a budget are the predictable ones nobody budgets for. Sinking funds fix that with simple division; here's the full math.
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06
Fix Credit Report Errors: A Step-by-Step Guide
Wrong balances, mystery accounts, debts that will not die: how to find errors on your three credit reports and dispute them until they are actually fixed.
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07
Extended Warranties: When the Math Actually Works
The checkout counter pitch, decoded with arithmetic: what an extended warranty must pay out for it to beat simply self-insuring, and the few cases where it genuinely does.
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08
The Real Cost of Credit Card Minimum Payments
The minimum payment is engineered to keep the balance alive, not to end it. A full worked example at a 22.9% APR shows 125 years of payments and $92,000 of interest — and the two moves that collapse the timeline.
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09
Annual vs Monthly Insurance Payments: The Real Math
Paying insurance monthly can cost 5–15% more per year. A worked example on a $1,200 policy shows when the installment fee wins anyway — and the exact break-even fee rate where it does not.
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10
What Your Credit Score Actually Costs on a Mortgage
On a $350,000 30-year loan, the rate gap between credit tiers is worth six figures over the life of the mortgage. Here is the tier-by-tier arithmetic, where the cliffs are, and when chasing a higher score stops paying.
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11
Pay Off Debt or Invest? The Math, Done Honestly
Paying off a 22.9% credit card is a guaranteed 22.9% return; investing at an expected 7% is not guaranteed at all. Running both scenarios side by side shows exactly where the crossover is — and why the answer is mostly about interest rates.
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12
Roth vs. Traditional 401(k): The Break-Even Math
The entire Roth-versus-traditional question reduces to one comparison: your marginal tax rate today versus your effective rate in withdrawal. Here is the algebra that proves it, the dollar outcomes at each rate pair, and where the equal-tax theorem breaks.
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13
Renting vs. Buying: How to Find Your Actual Break-Even Year
Comparing a mortgage payment to rent flatters buying, because most of what ownership costs hides outside that payment. Here is a full break-even model with every number shown.
9 min Home & Mortgage -
14
Whole Life vs. Term Life: What the Premium Gap Actually Buys
A $500,000 term policy and a $500,000 whole life policy insure the same life. The difference is roughly $109,000 in premiums over 20 years. Here is what that money actually returns.
9 min Insurance -
15
The 401(k) Match Is a Guaranteed Return. Here Is What Skipping It Costs.
A dollar-for-dollar employer match is a 100% return before your money is invested anywhere. Running the numbers on a $62,000 salary shows exactly what contributing under the match threshold gives up.
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16
Closing Costs Explained: The Money Beyond the Down Payment
On a $350,000 home with 20% down, closing costs and prepaids add about $10,900 on top of the down payment. Here is the line-by-line math, and which parts you can actually negotiate.
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17
MVNO Phone Plans: The $1,020-a-Year Switch, in Numbers
A family of three on a major carrier's premium unlimited plan pays about $160 a month. The same three lines on an MVNO run about $75 — with real trade-offs you can test before committing.
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18
How Much Term Life Insurance You Need: The DIME Math
Rules of thumb like "ten times your salary" hide the real calculation. A 35-year-old with a $240,000 mortgage and two kids lands near $1 million of coverage. Here is the worksheet.
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19
CD Ladder vs. High-Yield Savings: The Three-Year Math, Run Both Ways
A CD ladder usually pays more than a savings account — but not always. We run $15,000 through both over three years, including the rate-cut scenario where the ladder wins big.
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20
Raising Your Insurance Deductible: When the Math Actually Works
"Just raise your deductible" is the oldest money advice on the internet. Here is the actual break-even math for $500 vs $1,000 vs $2,500, including the expected-value version and the two cases where it backfires.
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21
Extra Mortgage Payments: Exactly What $100 a Month Does to a 30-Year Loan
An extra $100 a month on a $340,000 mortgage at 6.25% cuts 3.5 years and $58,000 of interest. Full amortization tables for $100, $200, $400 and the 13th-payment trick — plus when investing beats prepaying.
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22
How Tax Brackets Actually Work (and Why a Raise Never Costs You Money)
A dollar-for-dollar walkthrough of the 2025 US federal brackets: what a marginal rate means, what a $58,000 salary actually pays, and the arithmetic behind the "a raise pushed me into a higher bracket" myth.
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23
The Real Math on Balance Transfer Cards: When a 3% Fee Beats 22.9% APR
A $6,200 balance costs $2,278 in interest at 22.9% APR — or $186 with a balance transfer fee, if the payoff actually happens inside the promo window. Every number, including the trap that turns the fee into $8,806.
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24
What a Used Car Really Costs Per Year: Every Line Item, With Numbers
A $18,000 used car financed at 8.2% costs $366.70 a month — and about $501 a month on top of that. Fuel, insurance, maintenance, tires, depreciation and registration, line by line, so the budget matches reality.
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25
Debt Avalanche vs. Debt Snowball: We Ran the Numbers on Both
Same $14,000 of debt, same $750 monthly budget: the avalanche saves $422 in interest, the snowball closes two accounts sooner. Here is the month-by-month arithmetic behind both, including what minimum-only payments really cost.
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26
What a High-Yield Savings Account Actually Earns You
A 4.00% APY account pays $400 a year on $10,000; a typical branch-bank rate pays $46. The full math on compounding, taxes, variable rates, and when a savings account is the wrong tool entirely.
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27
Credit Utilization: The Number That Moves Your Score in Weeks
Utilization drives 30% of a FICO score and resets every month. The per-card and overall math, why the statement date matters more than the due date, and the 30-day plan before a big application.
9 min Credit -
28
How to Build a Budget That Survives Real Life
Most budgets fail in week three, not week one. Here is a monthly system built around irregular income, annual bills and the spending you are not going to stop doing.
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29
How to Cut Subscription Costs Without Losing What You Actually Use
The average household now pays for far more recurring services than it can name. A practical audit, plus the cancellation traps that keep charges running after you think you have stopped them.
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30
Your Emergency Fund: How Much Is Actually Enough?
Three to six months of expenses is the standard answer. For most people it is either the wrong number or the right number for the wrong reason. Here is how to size it properly.