CalcRegistry
Blog
Guides, explainers, and tips to help you get the most out of our free calculators and converters.
Average American mortgage debt by state (2026)
Average mortgage balances by state from Experian (Q1 2025), plus national mortgage totals from the New York Fed (Q4 2025), FHFA conforming loan limits, and MBA delinquency figures.
Age difference vs age gap: same numbers, different conversations
How people use age difference vs age gap, what stays fixed on the calendar (and what doesn’t), and when plain date math is enough. Links to CalcRegistry’s age difference calculator.
Why planes fly in curves: the geometry of great-circle routes
Why do flight paths arc toward the poles instead of crossing oceans in a straight line? Great-circle distance, the Haversine formula, and the geometry of a sphere explained.
Social Security: the one retirement decision where waiting actually pays off
Social Security claiming age explained: benefits calculation, 62 vs delaying to 70, breakeven timing, federal taxes, couples, calculators to model retirement.
BMR vs TDEE for Weight Loss: How Far Below Maintenance Should You Eat?
Where the cutting preset fits, when it doesn't, and why eating below your BMR usually backfires. A plain-English look at maintenance calories and sane deficits.
Astrophotography without star trails: the 500 rule, the NPF rule, and a practical ceiling
Why stars smear, how the 500 rule and NPF rule cap your shutter, what declination and pixel pitch have to do with it, and how to get a number you can use on your next clear night. Includes our free calculator.
What Going Back to the Office Really Costs (and How to Put a Number on It)
Employers keep revisiting hybrid and return-to-office plans. Here's how to see past the gas pump and count what commuting actually takes from your year, including time.
Sensor size and crop factor: why your 50 mm lens doesn't always feel like a 50
A practical look at crop factor, full-frame as a reference, and what really changes when you swap sensor sizes. Framing, depth of field, noise, and when the math matters in real shoots.
Neutral density filters: the slow-shutter look, even when the sun won't cooperate
Friendly guide to ND filters for silky water and long exposures when the sun won’t cooperate. How stops work, how to think about shutter time, and a calculator that matches the math.
How Much to Tip at Restaurants, on Delivery, and When the Check Gets Split
Practical tipping math for sit-down meals, delivery apps, and group checks: what percentages usually mean, whether to tip before or after tax, and how to split fairly without a fight.