Real exchange rate calculator

Input contract, response fields, and validation rules

Optionally send decimals as an integer from zero through twelve (default six) to control half-up rounding on every computed field. All three levels must be strictly greater than zero: a zero or negative price would make the ratio undefined or meaningless for purchasing-power comparison, and a non-positive nominal rate is rejected for the same classroom domain. POST a JSON body with three required finite numbers: nominal_rate (domestic currency per one foreign unit), domestic_price (home price level P), and foreign_price (abroad price level P*). Missing fields, empty strings, non-finite values, and non-integer decimals outside the allowed range fail with invalid_input and are not billed. Common aliases are accepted: e, spot, nominal, fx_rate, or exchange_rate for nominal_rate; p_home, p_domestic, home_price, or p for domestic_price; p_foreign, p_star, abroad_price, or p_star_foreign for foreign_price. On success the body returns the echoed inputs (rounded), price_ratio as foreign over domestic, real_exchange_rate as nominal times that ratio, ppp_gap_percent as (price_ratio minus one) times one hundred, price_level_band as a coarse classroom label (domestic_prices_higher, equal_price_levels, or foreign_prices_higher), and formula. Example: nominal twenty, domestic one hundred, foreign one hundred twenty yields price_ratio one point two, real exchange rate twenty-four, ppp_gap_percent twenty, and foreign_prices_higher. Pair the numbers with your own multi-period table if you need period-to-period real appreciation as the percent change in the real rate; this endpoint computes only the level for a single triple and does not re-base historical series or convert CPI into GDP deflators.

Where a real exchange rate API earns its keep

Principles and intermediate open-economy courses use a real exchange rate calculator so students can convert any valid nominal rate and two price levels into the canonical relative-price measure without confusing quote conventions or mixing CPI with spot FX alone. Exam generators and LMS plugins need a deterministic oracle that rejects zero or negative prices instead of inventing a hollow real rate that a buggy grader might treat as parity. Failed validation does not consume balance. Trade and macro notebooks often recompute textbook tables from published CPI and mid-market quotes; pinning the arithmetic in a tiny parse API keeps spreadsheet drift out of the comparison column. Keep requests small, pin the rounded real_exchange_rate and ppp_gap_percent fields in tests, and you get reproducible relative purchasing-power numbers for homework, LMS plugins, and edge workers without standing up a full multi-country national-accounts pipeline of your own.