That is just a coincidence (decimal ending in "5"), plus the fact that `.to_d` does some cleanup preprocessing. Counterexample: BigDecimal("1.59999999999999

That is just a coincidence (decimal ending in "5"), plus the fact that `.to_d` does some cleanup preprocessing. Counterexample: BigDecimal("1.5999999999999996") == 1.5999999999999996.to_d => false The most ergonomic way to initialize decimal numbers is IMO "123.45".to_d (Note the quotes around the number. `.to_d` is being called on a string.) BigDecimal's only lossless API is through strings. It would be nice to have native support for decimals at the parser level: 0d123.45 => BigDecimal("123.45")