Salary Calculator — hourly, weekly, monthly & annual converter

The calculator converts a salary from one pay period into every other pay period by anchoring on an annual equivalentand deriving every other period from that single number using the standard payroll multipliers used by the US IRS, UK HMRC, and Sri Lanka's Department of Labour. The flow has three steps:

1. Convert the input to an annual figure. annual = monthly × 12 = bi-weekly × 26 = semi-monthly × 24 = weekly × weeks/yr = hourly × hours/wk × weeks/yr. The monthly, bi-weekly, and semi-monthly multipliers are fixed by payroll convention; the weekly and hourly conversions depend on the hours-per-week and weeks-per-year you enter.
2. Derive every period from that annual figure. monthly = annual / 12, weekly = annual / weeks/yr, hourly = annual / (hours/wk × weeks/yr), and so on. Anchoring on the annual figure keeps every period internally consistent — multiplying any output back by its payroll constant returns the same annual figure to within floating-point noise.
3. Apply the optional deduction. If you enter a combined tax + social rate, the calculator multiplies every gross figure by 1 − rate to estimate take-home. This is a flat-rate approximation — real income tax is progressive, so use your effective tax rate (total tax / total income), not your marginal rate.

The annual-as-anchor approach matters because a calendar year has ~52.18 weeks but only exactly 12 months. Multiplying weekly pay by 4 to estimate monthly underestimates by roughly 8%; multiplying by 52 / 12 ≈ 4.333 is correct. Every payroll spreadsheet, government tax form, and accounting standard uses this convention.

The calculator includes a round-trip check: after deriving all periods from the annual figure, it re-reads the value in the user's input period and confirms it matches the original input. A mismatch would indicate an arithmetic bug — the “round-trip verified” badge in the calculator card confirms this passed for your inputs.

• U.S. Bureau of Labor Statistics — Occupational Employment & Wages methodology
• IRS Publication 15-T — Federal Income Tax Withholding Methods (payroll periods)
• HM Revenue & Customs — Working out an annual rate of pay
• Sri Lanka Department of Labour — Wages Boards Ordinance (Cap. 136)

The 12 / 24 / 26 monthly, semi-monthly, and bi-weekly multipliers are fixed by US, UK, and EU payroll convention and do not change year-to-year. Hours-per-week and weeks-per-year defaults are country-specific full-time conventions. Last cross-checked on 2026-05-11.