OPT_FORWARD_START Function (Gnumeric)

=OPT_FORWARD_START(flag,spot,alpha,time_start,time,rate,volatility,carry)

OPT_FORWARD_START values an option whose strike is set later as alpha times the asset price at the start date. This differs from a vanilla option with a cash strike fixed today. The output is a theoretical present value in the same currency units as spot.

All eight arguments are required. Flag is “c” for a call or “p” for a put. Spot is today’s positive asset price; alpha is the positive strike multiplier (1 means at-the-money at the future start). Time_start is the interval until the strike is set, and time is the interval from today to final maturity. Rate is the continuously compounded risk-free rate; volatility is annualized standard deviation; carry is the net annual cost of holding the asset, often rate minus dividend yield. Enter 5% as 0.05.

The inspected help labels the times as days, but the callback performs no day-to-year conversion: it uses time minus time_start directly inside Black–Scholes and an exponential involving carry minus rate. With annual rates and volatility, use years consistently. Require 0 <= time_start < time and positive volatility; boundary limits were not executed.

The first formula below sets the strike three months from now and expires one year from now. With carry equal to rate, the start-date prefactor is one. Independent Black–Scholes homogeneity reduces the example to a current-spot/current-strike option with 0.75 years remaining. The call is approximately 8.772268259757 and the put 5.091710031839.

Doubling spot from 100 to 200 while holding alpha fixed doubles the result, as the third fixture confirms. This is a useful model check: alpha is dimensionless, not a cash strike of 1. For a sensitivity worksheet, put start intervals in A2:A5 and use =OPT_FORWARD_START("c",100,1,A2,1,0.05,0.2,0.05) in B2, filling down only for starts strictly below 1. These additional timing scenarios are instructions for analysis, not separately recorded native results.

The tested invalid flag returns #NUM!. Check units and the order of volatility and carry before treating an unexpected price as a market insight. A missing required argument is not an invitation to use another program’s default. Negative time differences, zero volatility and nonpositive alpha are outside this guide’s tested domain; avoid evaluating singular formulas merely to discover their error text. No transaction costs, exercise policy customization or calibration is provided by this function.

• =OPT_FORWARD_START("c",100,1,0.25,1,0.05,0.2,0.05) → 8.772268259756933
• =OPT_FORWARD_START("p",100,1,0.25,1,0.05,0.2,0.05) → 5.091710031839125
• =OPT_FORWARD_START("c",200,1,0.25,1,0.05,0.2,0.05) → 17.544536519513866
• =OPT_FORWARD_START("bad",100,1,0.25,1,0.05,0.2,0.05) → #NUM!

The introduction release is not established by the retained evidence. The retained implementation and bounded native evidence are Gnumeric 1.12.57. No retirement or last functioning release is established. Function availability, argument defaults and numerical algorithms can differ in other spreadsheets; test exported workbooks in the receiving application rather than treating the name as a compatibility guarantee. These are synthetic calculation examples, not investment recommendations.

Native ssconvert recalculated the saved workbook on 17 October 2026 at 02:45 UTC. Input formulas, saved output cells and evidence-file hashes were rechecked after recovery. The 4 records above are engine evidence, not GUI screenshots. No new execution, untested extreme case or newer-version execution is claimed.

• Gnumeric 1.12.57 implementation and argument registration
• Official function catalog

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