About & Methodology

The problem with most calculators

Type "rent vs. buy calculator" into Google and you'll find dozens of tools. Most return a monthly payment number, or a break-even year buried in a table with 15 rows of data. You're left doing the interpretation yourself — which is the hard part.

The same is true for job offer comparisons, health insurance decisions, and retirement planning. The math isn't the hard part. The hard part is knowing what the math means for your specific situation.

Finlybox was built around one principle: every tool ends with a verdict. Not just a number — a clear, plain-English recommendation that tells you what to do next.

Our methodology

Every calculator on Finlybox is built using the same framework:

Include every significant variable — especially the ones other calculators skip, like opportunity cost, commute time value, and long-run maintenance.
Use current data — rates, tax brackets, and cost benchmarks are reviewed and updated quarterly.
Run calculations client-side — all math happens in your browser. We never see your inputs.
Source every assumption — if we use a benchmark figure, we cite the source below.

Key assumptions by calculator

Calculator	Key assumptions	Source
Rent vs. Buy	3% annual rent increase; 1% annual maintenance; 3% buying closing costs, 6% selling	NAR, Census Bureau
Job Offer	IRS mileage rate $0.67/mile; 50 working weeks/year; daily rate = salary ÷ 260	IRS Rev. Proc. 2025-9
HDHP vs. PPO	HSA contribution limit $4,300 individual / $8,550 family for 2026	IRS Publication 969
Retire Early	4% safe withdrawal rate (Bengen Rule); 7% real stock market return assumption	Journal of Financial Planning
Buy vs. Lease	Average depreciation 15–25% year 1, 10–15% subsequent years by vehicle class	Edmunds depreciation data

What Finlybox is not

Finlybox is an educational tool, not a financial advisor. Our calculators are designed to help you think more clearly about major decisions — not to replace professional advice.

For decisions involving significant money, tax implications, or legal consequences, we always recommend consulting a qualified professional. Our "Talk to a fee-only advisor" sidebar links specifically to fee-only advisors — paid by you, not by commissions, so their incentives align with yours.

Sponsorships and advertising

Finlybox is free because of sponsored placements. Every sponsored unit is clearly labeled "Sponsored" and placed contextually — a mortgage rate comparison on the housing page, salary data on the career page, and so on.

Sponsors do not influence calculator methodology, results, or editorial content. Our verdicts are determined entirely by the math, not by who's advertising.

We participate in affiliate programs including LendingTree, SmartAsset, and Amazon Associates. When you click a sponsored link and take an action, we may earn a commission — at no cost to you.

Updates and accuracy

Rate benchmarks, tax figures, and cost assumptions are reviewed every quarter. Each calculator page shows its last-updated date. If you spot an error or an outdated figure, please reach out — we take accuracy seriously.