Mental math at work rarely looks like a worksheet — it's a quick split of a bill, a fast sanity check on a budget line, an on-the-spot estimate in a meeting. Being fast and confident with it is a small, real edge.
Splitting an invoice three ways before the client asks. Rounding a discount to check a quote looks right before you send it. Doing a rough percentage in your head instead of stalling a meeting to find a calculator.
None of these need advanced math — they need speed and confidence with the basics, which is exactly what erodes without use.
You don't need a study plan for this — a single 60-second Race round during a coffee break is enough to keep the recall sharp, and it's short enough to genuinely fit between meetings.
Check Stats occasionally rather than daily; the trend over a few weeks is what tells you whether it's working.