The Smart Kit Now Blog
Plain-English guides on money, health, home projects, and everyday math — each one paired with a free calculator so you can run the numbers yourself.
BMI for 5'4" and 150 Pounds: What It Means
At 5'4" and 150 pounds, BMI comes out to 25.7 — just 0.7 points into the overweight range — and the first weight at that height that actually reads "Overweight" is 145.4 pounds, not a round number.
Read the guideHow Much Extra to Pay Off a Car Loan in 3 Years
Add $276.90 a month to a $25,000 car loan at 7% APR and it's paid off in 3 years instead of 5. Here's the exact math, plus what smaller extra payments get you.
Read the guideHow Long to Double Your Money at 7 Percent Interest?
The Rule of 72 says 10.29 years. The exact math says 10.245 years. Here's the formula, a $10,000 worked example, and an accuracy table by interest rate.
Read the guideHow Much Does PMI Add to a $300K Mortgage Payment?
PMI on a $300,000 home runs $159 to $178 a month at a representative 0.75% rate, depending on your down payment, and disappears automatically once your balance hits 78% of the price. Here's the math by down payment size.
Read the guideHow Much Interest Will You Pay on a $50,000 Student Loan?
A $50,000 student loan disbursed on or after July 1, 2026 now defaults to a 20-year term, not 10 — at 6.52% that is $39,610 in interest. See the tier table, the $1 cliff, and how to pay less.
Read the guideWhat Body Fat Percentage Do You Need to See Abs?
The body fat percentage you need to see abs is about 10-14% for men and 16-19% for women — here's the full breakdown plus two step-by-step worked weight-loss timelines.
Read the guideHow Much Extra to Pay Off a 30-Year Mortgage in 20 Years
On a $300,000 loan at 6.5%, one extra $341 payment a month turns a 30-year mortgage into a 20-year one and saves about $145,822 in interest. Here's the math and a table of smaller amounts.
Read the guideDaily vs Monthly Compounding Interest: Does It Matter?
Daily vs monthly compounding interest differs by only a few dollars on typical savings balances, but the gap widens with time and rate. Here's the exact dollar difference, worked out.
Read the guideHow Many Fewer Calories Do You Need After 50?
The Mifflin-St Jeor formula shows BMR drops 5 calories for every year of age — about 100 fewer a day by 50, 200 by 70 — and why the popular 3,500-calorie rule overstates what unchanged eating habits actually cost you.
Read the guideCost to Drywall a 400 Square Foot Basement
Materials to drywall a 400 sq ft basement run about $340–$466 for walls only, or $609–$735 with the ceiling — installed by a pro, about $882–$2,058 walls only, or $1,482–$3,458 with the ceiling.
Read the guideHow Many Bags of Concrete for a 10x10 Patio?
For a 10x10 patio poured 4 inches thick, you need 62 bags of 80-lb concrete, 82 bags of 60-lb, or 123 bags of 40-lb — here's the math and when ready-mix wins instead.
Read the guideHow Much to Invest Monthly to Retire With $1 Million
The compound interest formula solved backward: exactly how much to invest each month to reach $1 million, broken down by the age you start and the return rate you assume.
Read the guideHow Much Interest in the First 5 Years of a Mortgage?
On a $350,000, 6.75% 30-year mortgage, 84% of every dollar paid in the first 5 years is interest — $114,771 of $136,206 paid, and the balance has only fallen to $328,565.
Read the guideBiweekly vs Monthly Mortgage Payments on a $300K Loan
A $300,000 mortgage at 6.5% paid true biweekly instead of monthly pays off in about 24 years, not 30, saving roughly $88,122 in interest — but one popular 'biweekly' plan saves nothing at all.
Read the guideHow Much Car Can I Afford on a $50,000 Salary?
The 20/4/10 rule caps car costs at 10% of gross income — and once real 2026 insurance rates are subtracted, a $50,000 salary supports about $11,310, not the $20,000+ most quick explainers imply.
Read the guideHow Much House Can I Afford on a $70K Salary?
On a $70,000 salary the 28/36 rule caps your housing payment near $1,633 a month — enough for roughly $201,500 to $255,300 depending on your down payment. Here's the full breakdown.
Read the guideHow Much Does a 50-Mile Commute Cost Per Year?
A 50-mile round-trip commute costs about $3,228 a year in gas and maintenance for an average sedan — an EV charged at home cuts that to roughly $1,675. Here's the full math.
Read the guideMonthly Payment on a $20,000 Loan for 5 Years
At a representative 11.5% APR, a $20,000 loan over 5 years runs about $439.85 a month and $6,391 in total interest — see how rate tier and term length change that number.
Read the guideHow Many Calories to Gain 10 Pounds in 3 Months
The daily calorie surplus that adds up to 10 pounds over 90 days, a full worked TDEE example, and how your surplus pace decides how much of that weight is muscle.
Read the guideHow Many Calories to Lose 10 Pounds in a Month?
Losing 10 pounds in a month needs a 35,000-calorie deficit — about 1,167 a day. For most people that means eating below the safe calorie floor, so here's the math and a safer alternative.
Read the guideTotal Cost of Owning a $30,000 Car for 5 Years
The true 5-year cost of a $30,000 car is about $52,083 after resale value — a full line-by-line breakdown of financing, depreciation, insurance, fuel, and fees.
Read the guideHow to Calculate Body Fat Percentage With a Tape Measure
The U.S. Navy method turns three or four tape-measure readings into a body fat percentage — no calipers or scan needed, validated to within about 3.5 to 3.7 points of hydrostatic (underwater) weighing.
Read the guideStudent Loan Payment on a $45,000 Salary: What to Expect
On a $45,000 salary with $35,000 in federal loans, Standard repayment runs about $388.57 a month — IBR drops that to $175.50 and RAP to $150, though RAP alone actually pays down principal.
Read the guideHow Many Bricks Do I Need for a 200 Sq Ft Wall?
The exact math for how many bricks you need for a 200 square foot wall, by brick size, with waste margins and a full worked cost example.
Read the guideHow Much Gas Will a 500-Mile Road Trip Cost?
A 500-mile trip in an average sedan runs about $71.43 in gas at the August 2026 US average price — here's the exact math, cost by mpg, and how an EV compares on the same drive.
Read the guideIs Refinancing Worth It for a 1% Lower Rate?
A $302,000 balance at 7.25% dropping to 6.25% saves real money — but the term you pick changes whether refinancing wins or quietly costs you more.
Read the guideCompound Interest Explained: Why Ten Extra Years Beats a Bigger Contribution
The real math behind compound interest — how $200 a month grows differently depending on when you start, and why the same force makes debt grow just as fast.
Read the guideHow Many Sheets of Drywall for a 12x12 Room?
A 12x12 room with 8-ft ceilings needs 12 standard 4x8 sheets for the walls, waste included. Here's the exact math, a size-by-size breakdown, and the ceiling add-on.
Read the guideHow to Calculate Your BMI and What the Number Really Means
A clear guide to what body mass index measures, how to work it out yourself, why it isn't the whole story, and what to look at alongside it.
Read the guideDaily Calorie Needs Explained: BMR, TDEE, and How to Use Them
Understand the two numbers that decide your calorie target — your resting burn and your total daily burn — and how to turn them into a plan that works.
Read the guideHow Much Concrete Do I Need? A Slab Estimating Guide
Estimate concrete for a slab the right way — the volume formula, unit conversions, waste allowance, and how to avoid the two most costly ordering mistakes.
Read the guideElectric vs Gas Car: How to Compare the True 5-Year Cost
Sticker price is only the start. Here's how to build a fair five-year total-cost comparison between an EV and a gas car — fuel, maintenance, incentives, and depreciation.
Read the guideHow to Calculate Your Car Loan Payment (With a Real Example)
A $30,000 auto loan at 6.5% for 5 years runs about $587 a month. Here's the formula behind that number, a worked example, and how term and down payment change what you pay.
Read the guideHow Much House Can You Afford? The 28/36 Rule Explained
Lenders cap your housing payment at 28% of income and your total debt at 36% — whichever number is lower wins. Here's how to run both and see what actually limits your budget.
Read the guideHow to Calculate Your Mortgage Payment (With Real Examples)
A plain-English guide to how mortgage payments are calculated, what drives them up or down, and how to estimate yours in under a minute.
Read the guide