The Pet Weight tool estimates future weight from two observations of the same pet. Record an earlier age and weight, then a later age and weight, and choose a target age. The result extends the measured change in kilograms per age.
Model limitation: this is a linear estimate from your observations, not a verified Grow a Garden growth curve. It does not infer hatch weight, apply named pet classes or calculate trade prices. If boosts, mutations or game rules change between observations, collect a new pair under consistent conditions.
Inputs in the current tool
- Earlier weight and age: the first observation, such as 1.00 kg at age 1.
- Later weight and age: the second observation of that same pet, such as 1.20 kg at age 11.
- Target age: an age at or beyond your later observation, such as 21.
Weights must be positive. Ages must be non-negative whole numbers, the later age must exceed the earlier age, and the second weight cannot be lower than the first for this model. Empty fields are rejected rather than silently replaced with default assumptions.
Formula and a worked example
growth per age = (later weight − earlier weight) ÷ (later age − earlier age)projected weight = later weight + growth per age × (target age − later age)
Using illustrative observations of 1.00 kg at age 1 and 1.20 kg at age 11 gives (1.20 − 1.00) ÷ (11 − 1) = 0.02 kg per age. At target age 21, the estimate is 1.20 + 0.02 × 10 = 1.40 kg. Selecting target age 11 returns the measured 1.20 kg, which provides a useful baseline check.
Compare two observed growth rates
Suppose a second pet measures 2.00 kg at age 1 and 2.10 kg at age 11. Its measured rate is 0.01 kg per age, giving 2.20 kg at age 21. This pet remains heavier in the example, although the first pet gained weight faster over the observed interval. Neither result establishes ability strength or a fair trade value.
When to trust the estimate less
Extrapolation becomes less reliable when the target lies far beyond the observations. A short interval, rounded display values, an active boost ending, or a game update can all change the apparent rate. Begin with a nearby target and compare the prediction with a third actual observation before extending the estimate.
If the observed weight decreases, the current model asks for a new consistent observation pair. Do not erase a real decrease from your notes: investigate whether the pet, modifier or measurement conditions changed.
Keep the units separate
Weight uses kilograms; age is the game’s age value. XP is a different quantity. Use the XP Time Planner for a numeric XP target and measured XP gain. For an egg countdown, use the hatch-time tool.
Reporting a mismatch
Include both observed ages and weights, the target age, the displayed result and any change in boosts or game version. Separate an arithmetic error from an assumption that stopped matching the game. See the data and accuracy policy and contact page.
Revised September 6, 2026. This guide replaces earlier instructions describing controls that were not available in the live tool.
Use a third observation to check the projection
For the 1.00 kg at age 1 and 1.20 kg at age 11 example, the model projects 1.40 kg at age 21. If your third actual observation is 1.35 kg, the projection is 0.05 kg high, about 3.7% relative to that observation. That is evidence to remeasure the recent growth rate, rather than rounding the discrepancy away.
A flat pair of observations produces a flat estimate. It does not prove future growth has stopped. Very short intervals and rounded displayed weights can conceal small changes, so compare several observations under consistent conditions.