Weight loss and gain calculator

Calculate observed weight change, progress toward an entered comparison weight, and a straight-line time scenario.

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Weight loss and gain calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

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Starting weight (kg)

Current weight (kg)

More inputs and assumptions

Your chosen comparison weight (kg)

Elapsed weeks between measurements

Direction of comparison

Answer

…

Calculate observed weight change, progress toward an entered comparison weight, and a straight-line time scenario.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

This is arithmetic on your measurements and chosen comparison weight, not a calorie prescription, suitable-weight recommendation or biological forecast. Fluid changes, measurement conditions and changing trends affect weight. The time scenario assumes the same average change continues; it is not a promised or recommended schedule. Use consistent measurement conditions and discuss unexplained changes with a clinician.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

Check another calculation

Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.

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Updated 2026-09-29

Using Weight loss and gain calculator

Calculate observed weight change, progress toward an entered comparison weight, and a straight-line time scenario.

Next: Healthy weight calculator

Next: Calorie calculator

A worked example

For starting weight (kg) = 90, current weight (kg) = 85, your chosen comparison weight (kg) = 80, elapsed weeks between measurements = 10, direction of comparison = Weight loss, observed change (kg) = 5.

Before you use the result

Example results for starting weight (kg)

These examples use Current weight (kg): 85; Your chosen comparison weight (kg): 80; Elapsed weeks between measurements: 10; Direction of comparison: Weight loss. They are reference calculations, not recommended settings.

Starting weight (kg)	Observed change (kg)
90	5
180	95

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ToolOctopus. “Weight loss and gain calculator.” Updated 2026-09-29. https://tooloctopus.com/weight-loss-calculator.

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