Your operator sends a text a few days before a low-use number lapses: recharge now or lose it. For a SIM you keep only for OTPs and the odd missed call, that text is the whole relationship you have with the number. It also asks a different question from the one our other posts answer. Not which plan gets you the most data — which recharge keeps the number breathing for the least money.
The wrong instinct: buy what you'd buy for your main number
Most people recharge a second SIM the same way they recharge their first one, because that is the only recharge screen they know. Take a plan priced around 200 rupees, 28 days of validity, a gigabyte of data a day. Divide price by validity, as we explained in how cost per day works, and it comes out to roughly 7 rupees a day — a genuinely good rate, by the standard that post sets.
It is a good rate for the wrong product. On a number that receives three OTPs a month, that gigabyte a day is not a benefit. It is close to 28 gigabytes you paid for and never opened. The data allowance is the entire reason the plan costs what it costs, and you are throwing it away every day.
The number that actually matters for a second SIM
Strip the data out of the comparison and one number is left: rupees per day of validity. That's it. Not data per rupee, not calling minutes, not the SMS bundle — just how many days of "the number stays live" you're buying for how many rupees.
This is where a minimum recharge or validity-only recharge plan earns its keep. These packs carry little or no data and exist for exactly one job: keeping a number active and able to receive calls and texts. Compare two of them on price divided by days, the same arithmetic as any other plan, and the cheapest one per day of validity wins. There's no second variable to weigh against it.
Over-buying looks safe. It isn't.
Recharging a second SIM with a full monthly data plan feels like the cautious choice — more validity, more allowance, nothing to worry about. In practice it's the most expensive way to solve a problem that doesn't need solving. A number that only receives texts has no monthly data need at all, so every rupee spent on that allowance is a rupee spent on a feature you can't use. Buy validity. Buy validity again next time. Skip the rest.
Under-buying is the trap on the other side
The opposite mistake is worse: let the recharge slide, and the number goes inactive. How long a number stays reserved for you after that point is set by the operator, not by PlanPick, and it varies enough between Jio, Airtel, Vi and BSNL that repeating a figure here would be a guess wearing the costume of a fact. The text your operator sends is the only source that's current for your number — read that, not a forum post from two years ago.
What's not in doubt is the cost of getting it wrong. A lapsed number that gets reassigned takes with it every account that still uses it for OTPs — banking, email recovery, whatever you signed up for years ago and forgot about. Recovering access after that is slower and more annoying than any recharge would have been, and sometimes it isn't possible at all. A ten or twenty rupee difference in the recharge you skipped is not the number worth weighing against that.
What to buy instead
Look for the plan with the lowest price divided by validity among the packs that carry little or no data — not the lowest sticker price, and not the one with the most data thrown in as a bonus you'll never use. For what's on offer across operators right now, see all plans.
One number, recharged once every few weeks or months, no data attached — sized to match how rarely you touch that phone. Get it right once and the only reminder you need is the text your operator sends before the next one is due.